Fixed #13968 -- Fixed SelectDateWidget processing of an invalid date input value when USE_L10N is on, for consistency with its behavior when USE_L10N=False (now the form field reports the validation error in both cases). Thanks mitar for the report.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@15416 bcc190cf-cafb-0310-a4f2-bffc1f526a37