Fixed #9609 -- Modified the clean method of(Null)Boolean field to accept '1'...

Fixed #9609 -- Modified the clean method of(Null)Boolean field to accept '1' and '0' as valid inputs. Thanks to psagers for the patch.

This is required to support the use of non-default form widgets such as RadioSelect when the data comes from MySQL, which uses 1/0 to represent booleans.

Merge of r10660 from trunk.

git-svn-id: http://code.djangoproject.com/svn/django/branches/releases/1.0.X@10662 bcc190cf-cafb-0310-a4f2-bffc1f526a37