Add back date_format filter

This was not removed from the docs, so it should be supported for the
foreseeable future.

salt/utils/dateutils.py

@@ -60,6 +60,7 @@ def date_cast(date):
                 'Unable to parse {0}. Consider installing timelib'.format(date))
 
 
+@jinja_filter('date_format')
 @jinja_filter('strftime')
 def strftime(date=None, format="%Y-%m-%d"):
     '''