ros/genmsg — pull request #39 by v4hn (2014-02-04 18:40:22+00:00)
Title: Add an explanation to error on partial overlay

I spent 4 hours searching for the bug and possible workarounds before I
figured this one out:

Fatal Error: target _generate_messages_cpp already defined in module

We shouldn't really do anything here but error out, because it's a bad idea to
partially overlay the module in the new workspace - Everything in alphabet
before in the workspace which transitively relies on uses
the old one instead of the overlay..

But the old error message is pretty unhelpful and confusing.