Trying to patch the latest revision 72608 and it didnt work, here on winxp. 

C:\prg\Python30\Lib\idlelib>svn update
Restored 'IOBinding.py'
At revision 72608.

C:\prg\Python30\Lib\idlelib>patch IOBinding.py defaultextension.patch
--verbose
Hmm...  Looks like a unified diff to me...
The text leading up to this was:
--------------------------
|Index: Lib/idlelib/IOBinding.py
|===================================================================
|--- Lib/idlelib/IOBinding.py   (revision 72282)
|+++ Lib/idlelib/IOBinding.py   (working copy)
--------------------------
Patching file IOBinding.py using Plan A...
Hunk #1 succeeded at 480 (offset -45 lines).
Hmm...  Ignoring the trailing garbage.
done


If I do the patch by hand, it works. All files are saved with ext. .py.
When set 'defaultextension = ""', it is save well too, but then IDLE
crashed immediately.