Allow custom change commit messages by supplying a commit message and
optionally a changelog message as arguments.
* etc/committer.scm.in (break-string-with-newlines)
(custom-commit-message): New procedures.
(main)[change-commit-message*]: New sub-procedure. Use them.
(main): Use it.
Signed-off-by: Ludovic Courtès <ludo@gnu.org>