By default protobuffs doesn't create beams with debug info.  This
causes issues when running dialyzer which requires debug info.  Read
the `erl_opts` config and pass it down to protobuffs compiler.

The DirRef in the spec file is relative to the directory where the spec
file is located. ct2_rt was erroneously copying the spec file to test/.

eunit_test:function_wrapper/2 was renamed to eunit:mf_wrapper/2 in
R15B02. Ignore both calls like we do with escript:foldl/3.

Cover gets slower and slower for each application. This is due to the
cover_server internal state. Stopping the cover server between
eunit+cover runs, emptying the cover_server state, gives a ~5-6x speed
improvement when analyzing many Erlang modules. Stopping the cover
server replaces the earlier practice of doing a cover:reset before each
run. On a project consisting of 62 dependencies with a total of 1866
Erlang modules the running time of rebar eunit decreased from ~20
minutes to ~3 minutes.

* re-compile rebar.erl instead of rebar_core to define VCS_INFO
* append "-dirty" if vcs indicates unclean repo status

1. manually insert directory entries to work around issues fixed in
   R15B02 erl_prim_loader
2. put the escript archive's beams in appname/appname/ebin

Tested with R13B03 and R15B01.

Use erl_prim_loader:read_file_info instead of filelib:is_file to make
sure paths inside the escript archive are handled properly.