Fix circular import via lazy translation

EnhancedThreadedCommentFlag inherits from Auditable, which was importing
ugettext, which imports all models, including
EnhancedThreadedCommentFlag, which created a circular import. This is ok
in runserver, but crashes gunicorn. (I was able to get a stack trace
from gunicorn by editing the upstart job to include the --debug flag)
Merge pull request #1608 from jwalgran/topic/fix-circular-import-in-comment-mod

Fix circular import via lazy translation