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/pimp.py b/Lib/plat-mac/pimp.py
index b3138bd..5fc16f0 100644
--- a/Lib/plat-mac/pimp.py
+++ b/Lib/plat-mac/pimp.py
@@ -14,7 +14,7 @@
 """
 
 from warnings import warnpy3k
-warnpy3k("In 3.x, the pimp module is removed.")
+warnpy3k("In 3.x, the pimp module is removed.", stacklevel=2)
 
 import sys
 import os