Some other tests, when failing, don't always remove their TESTFN file.
Try to do it for them, so our mkdir() operation doesn't fail.
diff --git a/Lib/test/test_mailbox.py b/Lib/test/test_mailbox.py
index 382a42e..1d1a063 100644
--- a/Lib/test/test_mailbox.py
+++ b/Lib/test/test_mailbox.py
@@ -2,6 +2,12 @@
import os
import test_support
+# cleanup
+try:
+ os.unlink(test_support.TESTFN)
+except os.error:
+ pass
+
# create a new maildir mailbox to work with:
curdir = os.path.join(test_support.TESTFN, "cur")
newdir = os.path.join(test_support.TESTFN, "new")