(http://www.cygwin.com/faq/faq_3.html#SEC41).
Also check whether onerror has actually been called so this test will
fail on assertion instead of on trying to chmod a non-existent file.
the documented behavior: the function passed to the onerror()
handler can now also be os.listdir.
[I could've sworn I checked this in, but apparently I didn't, or it
got lost???]
and test_support.run_classtests() into run_unittest()
and use it wherever possible.
Also don't use "from test.test_support import ...", but
"from test import test_support" in a few spots.
From SF patch #662807.
Johannes Gijsbers
Tim Peters
Guido van Rossum
Brett Cannon
Walter Dörwald
Barry Warsaw