As Ludo' rightly points out, GitHub's patches are probably as stable
as their tarballs.
* gnu/packages/gimp.scm (gimp)[source]:
Use SEARCH-PATCHES instead of an origin.
* gnu/packages/patches/gimp-make-gegl-introspect-optional.patch:
New file.
* gnu/local.mk (dist_patch_DATA): Add it.
