Support gopkg.in

[Fale]

Reading http://labix.org/gopkg.in it seems like this could be an interesting (and hopfully easy, since are github-based) improvement. I think the only thing that should be added - packaging a github package - is if it is present in gopkg.in and if yes, add the right Provides parts

[zyga]

I'd like to bump this issue as gopkg.in is a very common place for golang packages.