[[Quilt http://savannah.nongnu.org/projects/quilt]] is a system for
managing changes to source code. To quote from the RPM package:
> These scripts allow one to manage a series of patches by keeping track
> of the changes each patch makes. Patches can be applied, un-applied,
> refreshed, etc.

I've played with quilt and it worked out nicely. Notably, it has
very useful support for easily adding more patches to an RPM (which
is already a base program version plus a stack of patches).

{{CutShort}}

Quilt is installed on gpu; see _quilt(1)_ for the man page and
_/usr/share/doc/quilt-0.40/quilt.pdf_ for a PDF paper on using
it.