Bu-bye, rebasing-merge.sh

It was discussed recently that it is rather confusing to keep that
script when we retired it in favor of merging-rebase.sh...

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
apply-from-gmane: accept permalinks, too

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
apply-from-gmane: fall back to three-way merges

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>