maint: GNUmakefile improvements.
maint: GNUmakefile improvements.

* GNUmakefile (unpack-distcheck-release): Be sure to rebuild rockspecs.
(check-in-release): Commit all unpacked files on the release branch.

Signed-off-by: Gary V. Vaughan <f9023000f29773649f3850298becb9544b5fd6a9@gnu.org>

gvvaughan/specl