[commit-patch-buffer.el] Adjust for Emacs 23 log-edit API.

I got errors when running commit-patch.  It looks like log-edit's
arguments changed meanings somewhere along the line (there's a comment
in the source).  I'm using GNU Emacs 23.1.50.1 (x86_64-pc-linux-gnu,
GTK+ Version 2.16.1) of 2009-07-31 on platinum, modified by Debian.
Here's a patch to fix it in my Emacs, but I didn't test with Emacs 22.