add force_permissive attribut to mandatory_warning for compatibility (not used in the code)

tiramisu/value.py

@@ -594,7 +594,7 @@ class Values(object):
     def del_information(self, key, raises=True):
         self._p_.del_information(key, raises)
 
-    def mandatory_warnings(self):
+    def mandatory_warnings(self, force_permissive=True):
         """convenience function to trace Options that are mandatory and
         where no value has been set