[RFC] patch's default backup behavior

Hello!

FreeBSD's patch follows historical patch(1) behavior w.r.t. backups,
where a backup is created for every file patched.

I'd like to test the waters on switching this to the GNU behavior,
which feels a whole lot more reasonable. Notably, they'll only create
backup files if a mismatch was detected (presumably this means either
a hunk needed fuzz or a hunk outright failed). This yields far fewer
backup files in the ideal scenario (context entirely matches), while
still leaving backup files when it's sensible (base file changed and
we might want to regenerate the patch).

Thoughts / comments / concerns? Cross-posted this to a couple of
different lists to try and hit the largest number of stakeholders in
patch(1) behavior.

Thanks,

Kyle Evans