Add an access abstraction (only array tests work, yet)

The access abstraction will be the new way of accessing builtin objects. This way it will be easier to move that to another process

jedi/evaluate/base_context.py

@@ -85,8 +85,13 @@ class Context(BaseContext):
         result = ContextSet()
 
         for index in index_contexts:
-            if isinstance(index, (CompiledObject, Slice)):
+            if isinstance(index, Slice):
                 index = index.obj
+            if isinstance(index, CompiledObject):
+                try:
+                    index = index.get_safe_value()
+                except ValueError:
+                    pass
 
             if type(index) not in (float, int, str, unicode, slice, type(Ellipsis)):
                 # If the index is not clearly defined, we have to get all the