patchwork is overenthusiastic about detecting start of diff

[Peter Maydell]

A recent patch I sent to qemu-devel is displayed misformatted
on patchwork.ozlabs.org:

http://patchwork.ozlabs.org/patch/82495/

apparently because one of the lines in the commit message
began with the word "different" and patchwork decided that
this marked the start of the diff...

I guess it should look for something that's a bit more
tightly constrained to being a real patch "diff" line.

-- PMM