[1.1.X] Fixed #13107: Adjusted decimal_places validation to accept 0 as a...

[1.1.X] Fixed #13107: Adjusted decimal_places validation to accept 0 as a valid value. Thanks to loewis for report. 

r12774 from trunk.


git-svn-id: http://code.djangoproject.com/svn/django/branches/releases/1.1.X@12775 bcc190cf-cafb-0310-a4f2-bffc1f526a37