evolve: factor out check for creating unstable commits This check is pretty non-trivial, and we do it in two places already. We're going to do it in a third place soon.

syntax: re
/figures/[^/]+\.png$
^html/
\.pyc$
~$
\.swp$
\.orig$
\.rej$
\.err$
^tests/easy_run.sh$
^build/
^MANIFEST$
^docs/tutorials/.*\.rst$
\.ico$