Here are some tweaks I have made to my ftyperc that others might find useful:
The first change replaces "_diff" with "diff", which I think is something you overlooked when applying a previous patch.
The next change adds a couple more first-line patterns for diff files. They attempt to match diffs output by CVS, like the one attached. Feel free to reject the one with the question mark if you think it is too general. It would be really nice if JOE could do this first line matching on the first line that gets piped in when piping into JOE.
The third change relaxes the first line pattern for Python in order to allow "#! /usr/bin/env python".