make: when mrproper, also remove Git tree unrelated files

When we really clean up everything, also remove crap files that do
not belong to the Git tree.

Signed-off-by: Daniel Borkmann <dborkman@redhat.com>
make: also credit involved people in mail message

Still untested, since we did not yet tag a release, but for now,
also credit all involved people in a particular release.

Signed-off-by: Daniel Borkmann <dborkman@redhat.com>