build plt automaticly when is missing
Add Katja to the package index
Merge branch 'package/katja' of git://github.com/nifoc/erlang.mk
Merge branch 'master' of git://github.com/andrzejsliwa/erlang.mk
Add error message before failing due to invalid dependency

If a dependency specified in DEPS is unknown or invalid (its VS
is not "git"), erlang.mk will fail. Now, add a human-readable
error message to help the user understand what the problem is.