"gem unpack" support in RPM's %setup macro

Hi guys, For a long time, I thought that it would be interesting to have .gem expansion support in %setup macro. This would simply our .spec files a bit. Finally, I gave a go to this idea and proposed this to RPM upstream [1]. Please let me know (preferably via the PR) if you can foresee any issues with this approach. Thanks. Vít [1] https://github.com/rpm-software-management/rpm/pull/27