simplify consistency validation

reorder function (logical order)
remove duplicate arity (context, config_bag, option_bag, ...)
master cannot have length lower than slave length

tiramisu/setting.py

@@ -165,6 +165,8 @@ class OptionBag:
         kwargs = {}
         option_bag = OptionBag()
         for key in self.__slots__:
+            if key == 'properties' and self.config_bag is undefined:
+                continue
             setattr(option_bag, key, getattr(self, key))
         return option_bag
 
@@ -188,6 +190,9 @@ class ConfigBag:
             return self.permissives
         raise KeyError('unknown key {} for ConfigBag'.format(key))  # pragma: no cover
 
+    def remove_warnings(self):
+        self.properties = frozenset(self.properties - {'warnings'})
+
     def remove_validation(self):
         self.properties = frozenset(self.properties - {'validator'})