Add memoize_function to cache and use it in fake.get_faked

The previously added test should now pass.

Fix #591

jedi/evaluate/compiled/fake.py

@@ -8,6 +8,7 @@ import os
 import inspect
 
 from jedi._compatibility import is_py3, builtins, unicode
+from jedi.cache import memoize_function
 from jedi.parser import Parser, load_grammar
 from jedi.parser import tree as pt
 from jedi.evaluate.helpers import FakeName
@@ -97,6 +98,7 @@ def _faked(module, obj, name):
             return search_scope(cls, name)
 
 
+@memoize_function
 def get_faked(module, obj, name=None):
     obj = obj.__class__ if is_class_instance(obj) else obj
     result = _faked(module, obj, name)