Generate shorter patch names

Not all commits are blessed with a really short first-line summary in
their commit messages. This means that we shouldn't blindly take the
entire first line of the comment, since that sometimes results in
truly spectacular patch names.

I chose 30 characters as a reasonable value, considering that we don't
yet have any tab-completion on patch names. There's probably not much
point in making it configurable.

Signed-off-by: Karl Hasselström <kha@treskal.com>