Implement __hash__ method for type_qualifiers_t class

Author: iMichka

pygccxml/declarations/cpptypes.py

@@ -926,6 +926,8 @@ def __eq__(self, other):
             and self.has_extern == other.has_extern \
             and self.has_mutable == other.has_mutable
 
+    __hash__ = object.__hash__
+
     def __ne__(self, other):
         return not self.__eq__(other)