[1.5.x] Fixed #19444 -- Clarified IGNORABLE_404_URLS documentation

List of compiled regular expression objects describing URLs that should be

ignored when reporting HTTP 404 errors via email (see

:doc:`/howto/error-reporting`). Use this if your site does not provide a

commonly requested file such as ``favicon.ico`` or ``robots.txt``, or if it

gets hammered by script kiddies.

:doc:`/howto/error-reporting`). Regular expressions are matched against

:meth:`request's full paths <django.http.HttpRequest.get_full_path>` (including

query string, if any). Use this if your site does not provide a commonly

requested file such as ``favicon.ico`` or ``robots.txt``, or if it gets

hammered by script kiddies.

This is only used if :setting:`SEND_BROKEN_LINK_EMAILS` is set to ``True`` and

``CommonMiddleware`` is installed (see :doc:`/topics/http/middleware`).