[1.0.X] Fixed #8966 -- Changed is_safe for length_is filter to False, since...

[1.0.X] Fixed #8966 -- Changed is_safe for length_is filter to False, since its return value is a boolean, not a string.

Thanks Thomas Steinacher, carljm, and SmileyChris.

Backport of r9291 from trunk.


git-svn-id: http://code.djangoproject.com/svn/django/branches/releases/1.0.X@9292 bcc190cf-cafb-0310-a4f2-bffc1f526a37