Issue #16218, #16414, #16444: Backport FS_NONASCII, TESTFN_UNDECODABLE,
TESTFN_NONASCII of test.support from Python 3.4. Backport tests on non-ASCII
paths.
(Merge 3.2) Issue #16218, #16414, #16444: Backport FS_NONASCII,
TESTFN_UNDECODABLE, TESTFN_NONASCII of test.support from Python 3.4. Backport
tests on non-ASCII paths.