Remove IsScope in favor of an is_scope function.

This function was partially implemented anway. Now we've also added a function called 'get_parent_scope', to make it easy to get a scope of a Call, Statement, whatever.

jedi/evaluate/finder.py

@@ -380,7 +380,7 @@ def check_flow_information(evaluator, flow, search_name_part, pos):
         return None
 
     result = []
-    if isinstance(flow, pr.IsScope):
+    if flow.is_scope():
         for ass in reversed(flow.asserts):
             if pos is None or ass.start_pos > pos:
                 continue