fixed setting `RELX_OUTPUT_DIR` from `RELX_OPTS`

This fix is imperfect: it only works if `-o $DIR` are the first args
in `RELX_OPTS`. It does not implicitly set the `RELX_OUTPUT_DIR` when
there is an arg other than `-o`, e.g. `--dev-mode`, leading
`RELX_OPTS`.
Change package index file format and deps handling

This commit adds two columns to the package index file: the
method used to retrieve the dependency (only git supported
at this point) and the preferred version (a commit or
equivalent in the case of git).

Now that all the necessary information is in the package
index file, the dep_* lines become optional. It is possible
to fetch dependencies by just listing it in the DEPS variable,
for example this would fetch both cowboy and jsx:

DEPS = cowboy jsx

The dep_* line can be used to override the defaults. It now
takes three values, the method used to retrieve the dependency,
the repository URL and the preferred version. The only change
from before is the first value being added.
Merge branch 'relx-output-dir-fix' of git://github.com/jtmoulia/erlang.mk
Add CC/CFLAGS OS type detection code to plugins/c_src.mk
Allow $DIALYZER_OPTS to add more source directories

The current ordering of args in the dialyzer command don't allow additional
source directories to be specified. Putting --no_native first allows the
beginning of the $DIALYZER_OPTS to specify additional directories of files
to be analyzed.
Merge branch 'jj1bdx-cc-cflags' of git://github.com/jj1bdx/erlang.mk
Merge branch 'patch-1' of git://github.com/jaynel/erlang.mk
Improve detection of dependency support for make
Merge branch 'patch-71' of git://github.com/andreineculau/erlang.mk
Added eper as a package
Merge branch 'eper_pkg' of git://github.com/th0114nd/erlang.mk
Autodetect CT SUITES
Merge branch 'auto-detect-ct-suites' of git://github.com/sedrik/erlang.mk
Use $(error ...) for pkg-search target
Fix a wrong target name
Make Dialyzer find source files recursively
Strip whitespace around the PROJECT variable
Add a requirement for a space-free path
Only autodetect if we have a test directory.
Merge branch 'missing-test-dir-bug' of git://github.com/sedrik/erlang.mk