Allow higher level makefile to specify ERL_LIBS
Added realpath to ebin in test run to prevent ct_run messages
Export PKG_FILE so only one gets downloaded

Thought I had committed that. Oops!
Add cowlib to packages
Merge branch 'master' of git://github.com/gegidoni/erlang.mk
Do not run tests if test directory does not exist
Merge branch 'master' of git://github.com/srstrong/erlang.mk