Update __all__ for cookielib, csv, os, and urllib2 for objects imported into
the module but exposed as part of the API.
diff --git a/Lib/weakref.py b/Lib/weakref.py
index 70b383e..78b74ad 100644
--- a/Lib/weakref.py
+++ b/Lib/weakref.py
@@ -26,7 +26,7 @@
 ProxyTypes = (ProxyType, CallableProxyType)
 
 __all__ = ["ref", "proxy", "getweakrefcount", "getweakrefs",
-           "WeakKeyDictionary", "ReferenceType", "ProxyType",
+           "WeakKeyDictionary", "ReferenceError", "ReferenceType", "ProxyType",
            "CallableProxyType", "ProxyTypes", "WeakValueDictionary"]