I’ve switched from the custom commit-email.pl script to the mailer.py from Subversion 1.4.6. Apart from one issue (svn.core.svn_path_canonicalize), it seems to work fine with Subversion 1.3.1. This time when I submitted the patches they actually appeared on upstream dev mailing list as well.
Anyway, as of now you’ll see the diffs of a commit right in the email as suggested by Gabriel Burt. It doesn’t diff .po files, nor deletions or binary files. A custom reply-to header can be set. Just email me if you want one (or email@example.com). The reply-to can be set per repository and it needs to be the development mailing list of the repository. By default the reply-to is empty (so you’ll mail the committer). Perhaps it should default to desktop-devel-list instead.