All hooks files which were identical in two groups (debianoid and
redhatoid) have been moved to the new hooks/common directory and now
have symbolic links to the according new files at their old locations.
All hooks files which were identical and had no second group of
identically named hook files have been moved to a new hooks/common
directory and now have symbolic links to the new single file at their
old locations.
Also slightly modified to make this work:
* Makefile: copy new hooks/common directory
* Some tests: ignore new hooks/common directory