Please don't use revision numbers on commit messages (and elsewhere).

[Óscar Fuentes]

A revision number only makes sense on the branch where it was created
(and this only after setting some options, as Emacs did.) If I'm reading
the VC log on a random branch and see "Fix breakage introduced by rXXXX"
and want to look at the referenced revision, I need to switch to trunk
and hope that XXXX corresponds to one of its revisions. If a series of
commits on a feature branch mentions one another by revison number,
after merging them into trunk (or into any other branch) those numbers
are wrong.

So, if you wish to refer to another revision on the commit message (or
anywhere else) please use the revision id, which is unique for every
commit.