Generate ChangeLog from git log
A git2cl tool exists and is packaged on debian, but as the current ChangeLog format includes revision numbers we'll need to drop that information for the new ChangeLog (no revision numbers in a git-only repo).
One possibility here is to save the old ChangeLog files into a subdirectory (doc/changelog?) and start with a fresh one starting from where the old one ends.
Another is to STOP checking the ChangeLog into the repository but always only generate it at "make dist" time, which may be a bit tricky to pass "make distcheck" (as it sets the sources read-only) but may set us free from future management issues.
This is propedeutic for moving the codebase from SVN to git.