This adds a flexible mechanism for filtering what request/traceback
information is shown in 500 error emails and logs. It also applies
screening to some views known to be sensitive e.g. views that handle
passwords.

Thanks to oaylanc for the report and many thanks to Julien Phalip for the
patch and the rest of the work on this.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@16339 bcc190cf-cafb-0310-a4f2-bffc1f526a37