This executes: check-debugging, check-interfaces, check-miscaptures,
find-trailing-spaces, check-umids, pyflakes.
Other changes:
* fix check-umids.py to take starting points. run it as `check-umids.py
src` instead of `check-umids.py src/allmydata/*.py`
* check-debugging: rewrite in python to run from tox: tox doesn't like
to run shell scripts.
* put check-interfaces.py last: it produces lots of warnings, but passes
anyways. The others only produce significant output if they fail.
