- use --verify to make sure rev param is a rev, and barf otherwise.
 - make it always output to stdout; no funny business with tee.
 - take optional branch head name to specify which branch to summarize.
 - show baserev in a human readable way.
 - do not depend on diffstat; use git-apply --stat instead.

Signed-off-by: Junio C Hamano <junkio@cox.net>