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/bundlebuilder.py b/Lib/plat-mac/bundlebuilder.py
index 46c17df..f0c7fc2 100755
--- a/Lib/plat-mac/bundlebuilder.py
+++ b/Lib/plat-mac/bundlebuilder.py
@@ -29,7 +29,7 @@
 
 
 from warnings import warnpy3k
-warnpy3k("In 3.x, the bundlebuilder module is removed.")
+warnpy3k("In 3.x, the bundlebuilder module is removed.", stacklevel=2)
 
 import sys
 import os, errno, shutil