ensure dest exists before copying to it and fix src_dirs symlinking

Priv and include dirs need the virtual symlink in order to preserve hook
functionality in some edge cases.

This would cause crashes on linux and force people to have a src_dirs
config that is strictly matching what is on the file system rather than
acting as a specification of those that are valid.

To compare, if lib_dirs worked the same, then any repo that did not both
have apps/ and lib/ would crash, as the spec mentions both options as
valid.

Display warnings when cache dirs are read-only

This should provide more help to users directly and avoid having them go
through opening tickets for help.

Fixes #1767

Clear all dialyzer errors

- this is done by adding a HiPE dependency
- also in this: adding a test for directories, and fixing some indent

Bump cth_readable to 1.3.4: restore eunit macro formatter

Reload apps running in shell with new config

Fix local upgrade etag handling

Since packages store etags on disk directly, the local install feature
can no longer depend on this; we instead port the etag feature back to
local providers only.

This patch makes it so that whenever the rebar3 shell has a new
configuration for an application that is already running and would be
restarted (without risking the stability of the node or functionality of
rebar_agent), we stop and restart the app.

Fix precedence rules of erl_opts for test profile

When adding the 'TEST' macro to the test profile, we mistakenly sourced
the erl_opts values from the base profile rather than the test profile
itself.

This means that in cases where the base profile set an option such as
'no_debug_info' and a profile overrode it with 'debug_info', the default
options would get injected within the test profile, and broke the
precedence rules, yielding incompatible values.

This patch fixes things by adding the macro to the values sourced from
the test profile itself, fixing the issue.

Display script errors

Let's bundle this with another PR

This will at least display the script that failed with the stacktrace
before failing as usual, but without altering the return value.

This should make the common failure path more user-friendly without
breaking any existing behaviour that may have relied on the script file
working. If there's any unexpected side-effect, it will be visual only
rather than blocking full builds if ?ABORT were used.

Fix various Dialyzer warnings

Some still remain from erl_type calls from Dialyzer, but most of them
are handled.

Decided to just ignore rebar_alias since playing with the type specs of
abstract code format is just a nightmare and hard to do cross-versions I
guess.

Handle Schema-less Proxy URLs in ENV vars

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

Make rebar3 work with dialyzer internally

We got funny interactions since PR #1656:

- the last `debug_info`-related option seen in a list of options after
  profile merge is kept, allowing later profiles from overtaking earlier
  ones
- if you go `rebar3 as a,b,c compile`, the options from profile A come
  before B, which come before C, so C's options win
- overrides are applied in order of profile as well, giving a priority
  to a later profile than an earlier one
- The values in overrides are prepended rather than suffixed to the
  existing list
- this means if we have to overrides adding options, such as `default`
  adding `no_debug_info', and `dialyze` adding `debug_info`, the
  results are `[debug_info]` as `dialyze` is applied first, and then
  `[no_debug_info, debug_info]` as `default` overrides are applied
- the final result is `no_debug_info` always winning when erl_opts are
  overriden specifically.

only `debug_info` options are going to suffer this, and in the context of
overrides. Other `erl_opts` should be fine. I'm not sure how that can be
fixed at all.

In the meanwhile, we can add support back while leaving the default to
not having debug information. This is done by:

- moving all `no_debug_info` options to the `prod` profile
- forcing `prod` to be called by `./bootstrap` so that most people keep
  getting no debug info
- anyone calling `rebar3 clean -a`  and then rebuilding with `rebar3
  escriptize` (i.e. rebar3 devs) get debug info going

This is up for review and discussion.

(#1741): Fix quotes in etag values

Bump cth_readable to 1.3.3

Fixes some lager warnings since config changes

Remove noisy debug message

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

sort-as: force an order on multiple profiles