allowing to override rebar location in makefile
Merge pull request #11 from marcelog/marcelog_overriding_rebar_location

allowing to override rebar location in makefile
Fixes a crash with multi-app projects when one of the app do not use CT.
Merge pull request #13 from sylane/fix_multi_app

Fixes a crash with multi-app projects when one of the app do not use CT.