Add partial support for Erlang/OTP 17

If the directory we're about to process contains
reltool.config[.script] and the command to be applied is
'generate', then it's safe to process. We do this to retain the
behavior of specifying {sub_dirs, ["rel"]} and have "rebar generate"
pick up rel/reltool.config[.script]. Without this workaround you'd
have to run "rebar -r generate" (which you don't want to do if you
have deps or other sub_dirs) or "cd rel && rebar generate".

Allow rebar to compile applications using Erlang/OTP 17 and older
versions.  This patch only provides partial support since the rebar
tool itself must be compiled using an Erlang/OTP version that is older
than 17.

This calls the 'p4' command-line tool to checkout and sync Perforce
trees. It involves significantly more special code in Rebar than
using 'git p4', but it eliminates the indirection of
Rebar->Git->Python->Perforce

Using the filename as a prefix is less readable and inconsistent with
the other log messages.

Before:

DEBUG: src/foo.erl depends on...

After:

DEBUG: Dependencies of src/foo.erl ...

Running 'rebar list-templates' can take quite a long time, when it has
to search the file system. To fix that, make list-templates not recurse
by default. To enable recursion, run 'rebar -r list-templates'.

Always-on recursive application of all rebar commands causes too many
issues. Recursive application is required for:
1. dealing with dependencies: get-deps, update-deps, and compile of deps
   right after get-deps or update-deps
2. projects with a riak-like apps/ project structure and dev process

The vast majority of projects are not structured like riak. Therefore,
moving forward it's best to (by default) restrict recursive behavior to
dealing with deps. This commit does that and also adds command line and
rebar.config options for controlling or configuring recursion. Also, we
introduce two meta commands: prepare-deps (equivalent to rebar -r
get-deps compile) and refresh-deps (equivalent to rebar -r update-deps
compile). riak-like projects can extend the list of recursive commands
(to include 'eunit' and 'compile') by adding
{recursive_cmds, [eunit, compile]} to rebar.config.

Fix typo in rebar_erlydtl_compiler

Allow specification of module dependencies for appups

Incorrect REMSH args when sname is used.

Fix #220 (Reported-by: Joseph Norton)

Repetition of environment variable definitions in child processes (ports)

When running 'rebar qc' or 'rebar eunit', we were erroneously fetching
erl_opts more than once.

test_compile/3 is used by eunit and qc, but the comment was only
referring to 'rebar eunit'.

CWD plugins regression

Speed up the compilation process v5

* update files
* fix Dialyzer warning
* unconditionally enable info fil
* clean-up inconsistencies
* use term_to_binary compression
* use try...catch instead of case...catch...of
* do not write build info file if the graph is unmodified
* store info file as <base_dir>/.rebarinfo
* properly support list of compile directives
* fix regressions:
 - Fix a bug in handling of files to compile first.
 - If a file that is depended upon itself depends on other files, make sure
   those are compiled first. While at it, rename variables for correctness.
   Reported-by: David Robakowski
 - Make sure that FirstFiles has no dupes and preserves the proper order.
 - headers referenced via -include_lib() were not properly resolved to absolute
   filenames
 - .erl files found in sub dirs of src_dirs were not properly resolved to
   absolute filenames

* Do not parse source files twice while checking for relationship.
* Keep files relationships in a graph.
* The option 'keep_build_info' is introduced. When set to 'true'
  the graph will be kept in ebin/.rebar.build.info and will be
  used by further compiler calls. The default is 'false'.

docs: fix #228

eunit: fix dialyzer warnings introduced in 03da5e0b

Document support for abbreviated commands

Adapt erlydtl compiler plugin to latest version of erlydtl

Add random_suite_order option to eunit command

Option takes either 'true' or a numeric seed value. If true is passed, a
random seed is generated and used. The numeric seed value is for
repeatability.

The idea here is to root out test suites that are order dependant, or
that fail in the presence of certain orderings.

allow suite[s] or test[s] as options for eunit and ct

Xref extra path

Added R16B01 and R16B02 to travis config.