I would be happy to commit and watch the buildbots, once I have confidence in the patch though.  Question: I noticed that the following was changed in Lib/test/regrtest.py:

-    with support.temp_cwd(TESTCWD, quiet=True):
+    with support.temp_cwd(quiet=True, path=TESTCWD):

But the corresponding change wasn't made in Lib/test/__main__.py (which I believe is the code path used by Geoff's `./python.exe -m test -j3` invocation):

http://hg.python.org/cpython/file/96f08a22f562/Lib/test/__main__.py#l12

Those two code chunks should really share code by the way (even the code comment is copied verbatim), which would help in not needing to update code in two places as in this issue/patch.  Perhaps that should even be done first as part of a separate issue (to separate this into smaller changes).