fixes so that erlang.mk compile works

erlang.mk has `-Werror` on by default, so the warnings were breaking the build, and relx was giving errors for .app.src.

I'll bet there was a good reason for commenting out those exports, but this is what I have to do to get it working with erlang.mk. I did remove `-Werror` from erlang.mk for awhile, but I actually kind of like it :)