Thanks for your patch!

Initial comments:

* test_pipes does not conform to PEP 8 (whitespace issues, line length, etc).
* SVN reports that test_pipes has inconsistent line endings.
* Calling os.path.exists() as a check before os.unlink() creates a race condition; just catch the exception.
* In the future, please include new files in the patch itself. "svn add" the file, then "svn diff" will include it when creating the diff.

Please address these issues.