Because the filter tests take non-zero time to pass, it's possible for one of

the timeuntil tests to fail because the pre-recorded "now" has moved on
sufficiently far from actual "now()". Fixed the one test that was failing for
me (the other timeuntil and timesince tests already have a small buffer built
in to guard against this problem).

The problem was revealed after [8535].


git-svn-id: http://code.djangoproject.com/svn/django/trunk@8556 bcc190cf-cafb-0310-a4f2-bffc1f526a37