Refactor references: Matching more names that might be related

Fixes davidhalter/jedi-vim#900.
See also davidhalter/jedi-vim#552.

jedi/inference/context.py

@@ -308,11 +308,14 @@ class ModuleContext(TreeContextMixin, ValueContext):
                 until_position=until_position,
                 origin_scope=origin_scope
             ),
-            GlobalNameFilter(self, self.tree_node),
+            self.get_global_filter(),
         )
         for f in filters:  # Python 2...
             yield f
 
+    def get_global_filter(self):
+        return GlobalNameFilter(self, self.tree_node)
+
     @property
     def string_names(self):
         return self._value.string_names