[1.0.X] Fixed #5748 -- Made floatformat filter round properly on all platforms...

[1.0.X] Fixed #5748 -- Made floatformat filter round properly on all platforms and handle NaN input correctly on Windows. Also added tests for these cases. Thanks for the report and initial patch to SmileyChris and PJCrosier.

[9369] from trunk.


git-svn-id: http://code.djangoproject.com/svn/django/branches/releases/1.0.X@9370 bcc190cf-cafb-0310-a4f2-bffc1f526a37