Prevent spurious leaks when running regrtest.py -R. There may be more

issues that crop up from time to time, but this change seems to have been
pretty stable (no spurious warnings) for about a week.

Other modules which use threads may require similar use of
threading_setup/threading_cleanup from test_support.

Lib/test/test_threadedtempfile.py

@@ -22,7 +22,7 @@ FILES_PER_THREAD = 50   # change w/ -f option
 
 import thread # If this fails, we can't test this module
 import threading
-from test.test_support import TestFailed
+from test.test_support import TestFailed, threading_setup, threading_cleanup
 import StringIO
 from traceback import print_exc
 import tempfile
@@ -48,6 +48,7 @@ class TempFileGreedy(threading.Thread):
 
 def test_main():
     threads = []
+    thread_info = threading_setup()
 
     print "Creating"
     for i in range(NUM_THREADS):
@@ -72,6 +73,7 @@ def test_main():
     if errors:
         raise TestFailed(msg)
 
+    threading_cleanup(*thread_info)
 
 if __name__ == "__main__":
     import sys, getopt