Generate diff files for pacakges once patches have been applied

[Marco Trevisan (Treviño)]

Many times we upload the same package where patches that were previously applied as distro-patches have then been applied upstream.

This is currently generating a diff file that is more complex than needed and it's not easy to spot what really changed (for example when a patch has been applied upstream but with differences).

So, ideally when a package is uploaded and it (and/or the previous) contains patches, it would be nice to get the diff of the content once `quilt push -a` is called, minus debian/patches.