We can probably still move ahead without a cache if we must

We've had multiple tickets opened because of unclear PROXY settings when
the scheme is missing form the URI. To be helpful, we instead add them
dynamically whenever they're missing.

Example issues:
- https://github.com/erlang/rebar3/issues/1747
- https://github.com/erlang/rebar3/issues/1697

It makes things worse than if it weren't there.
Fixes issue #1726

This reverts commit 0f7e6c31e9.

This reverts commit 4ad1db9733.

This reverts commit 3f8dd5eace.

The way arguments are passed by the alias provider is not compatible
with all rebar providers/commands. Especially the release (relx)
provider does not like getting its arguments as a plain string. It
expects its arguments in a pre-parsed format as returned by
getopt:parse/2.

Other commands, e.g. eunit, seem to be fine with both ways of argument
passing. Therefore, this fix changes the alias provider argument passing
to the getopt format in general.

find_apps didn't read config files so no hooks were in the app_infos,
and now that hooks are being done rebar needs plugins to be able
to run clean plugin hooks in deps.

Although fairly irregular, the presence of a subdirectory in ebin/ while
running rebar3 escriptize would crash the run and generate a dump.

Since ebin subdirectories are generally not supported (adding a path for
an application only adds ebin/ and no subdirectories to the VM's path
set), we just silently ignore the directory altogether.

Fixes #1693

Rather than the caller having to think of what to purge or not, use
erlang:check_process_code/2 to detect if the caller (rebar3) may die
because of the operation.

If so, do a soft purge with a conditional delete instead of a hard purge
with a mandatory delete.

Prevents the killing of a plugin with itself

- Uses the code at https://github.com/tsloughter/rebar_alias and brings
  it within rebar3
- adds safety checks to prevent redefining built-in commands or obvious
  circular dependencies between commands (indirect circular deps are
  still possible)
- adds tests
- adds a systest to ensure no clash with the existing plugin

Has no ill effect as tested on Win10

The path reloading of plugins had been fixed properly, but the problem
is that the paths it was using to re-load only considered the current
compile step, rather than the overall state of plugins. As such, the
reloaded paths after plugin compilation only reloaded the *latest*
plugin and not the other ones.

This fix forces the addition of all built plugin paths to the code paths
after a plugin compile job is run. This ensures that the path is clean
for initial plugin deps (only add those that are required), and is
re-made total after the fact (add all the plugins possible).

This commit also includes a system tests suite that can be run
optionally; the problem with this plugin mechanism was impossible to
find through mocked dependencies, and a working counterexample was
provided to us. The systest suite can be run against real projects
without conflict to make sure no regressions are hit.

Adds an option (-m, --min_coverage, or {cover_opts, {min_coverage,X}})
to the 'cover' command, where the value is an integer between 0 and 100.

If the total coverage during the analysis is below the value received,
the command will fail with output like:

    ===> Requiring 64% coverage to pass. Only 62% obtained

If the rate is correct, the command silently passes as it currently
does.

This feature allows to enforce code coverage standards in a project if
desired.

This commit adds a common test hook along with the cth_readable stuff
whose role is to track failing test cases, and create a test
specification out of them.

The test specification is dumped on disk at
_build/<profile>/logs/retry.spec and can be accessed by calling
'rebar3 ct --retry'. This will auto-load the spec file if it can be
found and re-run the failing cases.

If any other argument is found on the list specifying tests, the
'--retry' argument is ignored.

All code for this is marked as experimental in case we end up (keeping
and then) dropping the feature.

This commit adds a common test hook along with the cth_readable stuff
whose role is to track failing test cases, and create a test
specification out of them.

The test specification is dumped on disk at
_build/<profile>/logs/retry.spec and can be accessed by calling
'rebar3 ct --retry'. This will auto-load the spec file if it can be
found and re-run the failing cases.

If any other argument is found on the list specifying tests, the
'--retry' argument is ignored.

All code for this is marked as experimental in case we end up (keeping
and then) dropping the feature.

The Erlang compiler runs based on a global state built from currently
loaded libraries and the configured code path that is available. For
this reason, the rebar3 compiler job unloads all plugin paths before
calling the Erlang compiler.

However, this causes a problem when an application uses a custom
resource handler with a dynamic version in their .app.src file since the
plugin that can be used to find the version has been unloaded.

Fortunately, the compile phase that runs the version handling is
distinct from the phase that uses the Erlang compiler. This patch fixes
the problem by re-loading the plugins' paths in memory before generating
the .app file, and before unloading them afterwards.

It appears that unloading them is unnecessary because the hooks after
that will re-load them, but it is likely better to play it safe with
that global state and clean up after ourselves. It offers better
protection for future changes.

Fixes #1657

Current rebar3 uses debug_info rules where debug_info is added by
default, and no_debug_info prevents the default from being added, and
removes any explicit debug_info, if any. The problem is that if
'no_debug_info' is anywhere in the config for a run, it cannot be
removed even with other profiles. additionally, no_debug_info ignores
special tuples like {debug_info, {Mod, Data}} and {debug_info_key, Key},
which can be used to add debug info and encrypt it (in lieu of plain
debug_info) respectively.

This patch makes it so that the following rules are in place:

- the last option seen takes priority, allowing profile overrides by
  the ordering rules the compiler expects
- the overriden options shall be explicitly deleted to avoid confusing
  the compiler
- any option related to debug info seen last cancels any no_debug_info
  that preceded it
- any no_debug_info option seen last cancels all of the other
  debug_info options
- if debug_info is seen last, it cancels out {debug_info_key, Key}
- if {debug_info_key, Key} is seen last, it cancels out debug_info
- All other options are left untouched in that context (defines can
  still be expanded and so on)

This should allow proper profile rules to be followed. Note that erl_opt
profile merging puts precedence on the *last* element of a list, to
match the compiler.

When fetching deps, if this is a clean repo there will be extensive
messages warning that dependencies which have already been fetched are
being skipped. For large projects being built and tested in a clean
environment this significantly increases the noise level of the build.

This modification adds an additional rebar option
(deps_warning_on_conflict) that will allow disabling these warning
messages. If deps_error_on_conflict is set, an error will still be
thrown. This will not change default behaviour of rebar.

There is a similar outstanding issue:
https://github.com/erlang/rebar3/issues/1105
However this seems to be a push for not outputting warnings when the dep
version is the same, rather than disabling warnings altogether.

Updates relx (windows fixes) and erlware commons (strings)

- OTP-21 readiness, Full Unicode support, massive dep upgrade
- fixed handling of proxy username and password when fetching registry
- git versions from tag made consistent and all strip 'v' prefix
- Prevent hard crash on duplicate plugin paths
- Fix include paths in profile multiapp edge case
- Fix unlock state carry, which broke do sequences with unlock in them.
- Avoid guessing on utf8 decoding of app files
- Various fixes related to .app files
- Warn user when an unsupported local git or hg resource is used
- Corrects a fix to src_dir values
- Update eunit_formatters to latest version
- Changes in wording of warnings for more accuracy