Autocomplete inherited methods when overriding in child class. Fixes #458.

test/completion/context.py

@@ -0,0 +1,22 @@
+class X():
+    def func(self, foo):
+        pass
+
+
+class Y(X):
+    def actual_function(self):
+        pass
+
+    #? []
+    def actual_function
+    #? ['func']
+    def f
+
+    #? []
+    def __class__
+
+    #? ['__repr__']
+    def __repr__
+
+    #? []
+    def mro