Use the memoize function for faked arguments only when needed.

It's important to note that memoizing every object would mean that
theoretically all objects passed through get_faked would get memoized. This
would have been a possible memory leak, which we should avoid.
Obviously the previous solution proposed in #649 was still better, but this
issue was a new one. Also using str() around keys was not a good idea.

Refs #649.

jedi/cache.py

@@ -91,18 +91,6 @@ def memoize_method(method):
     return wrapper
 
 
-def memoize_function(obj):
-    """ A normal memoize function for memoizing free functions. """
-    cache = obj.cache = {}
-
-    def memoizer(*args, **kwargs):
-        key = str(args) + str(kwargs)
-        if key not in cache:
-            cache[key] = obj(*args, **kwargs)
-        return cache[key]
-    return memoizer
-
-
 def cache_star_import(func):
     @time_cache("star_import_cache_validity")
     def wrapper(self):