There have been a handful of cases where orphaned compiled Python files (.pyc
files without an accompanying .py file) have been loaded preferentially by
the presubmit scripts, causing weird problems. This adds a check and a mode for
such files, either warning the user or deleting them.

BUG=None
TEST=local
  - Tested against local repository.

R=iannucci@chromium.org, szager@chromium.org

Review URL: https://codereview.chromium.org/621533002

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@292703 0039d316-1c4b-4281-b951-d872f2087c98