fix test_py3kwarns

The fact that this was failing and went unnoticed so long seems like a good argument for being able to enable and disble py3kwarnings through Python.
diff --git a/Lib/plat-mac/cfmfile.py b/Lib/plat-mac/cfmfile.py
index 309af87..ddbd468 100644
--- a/Lib/plat-mac/cfmfile.py
+++ b/Lib/plat-mac/cfmfile.py
@@ -6,8 +6,8 @@
 __author__ = "jvr"
 
 import warnings
-warnings.warn("the cfmfile module is deprecated and is removed in 3,0",
-              DeprecationWarning, 2)
+warnings.warnpy3k("the cfmfile module is deprecated and is removed in 3,0",
+              stacklevel=2)
 
 import Carbon.File
 import struct