Fixed #10604 -- Added note on the limitation of ungettext, especially as...

Fixed #10604 -- Added note on the limitation of ungettext, especially as relating to the {% blocktrans %} tag. Thanks to bartTC for the report, and Ramiro Morales for the patch.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@11164 bcc190cf-cafb-0310-a4f2-bffc1f526a37