topics: check for topic on commit before a user enters message
We have a enforce-topic cofig which can forbid user to commit without a topic on
it. We used to check topic on a commit after the user enters message, but we
should fail early.
syntax: re
/figures/[^/]+\.png$
^html/
\.pyc$
~$
\.swp$
\.orig$
\.rej$
\.err$
^tests/easy_run.sh$
^build/
^dist/
^MANIFEST$
^docs/tutorials/.*\.rst$
\.ico$
tests/\.testtimes