add proper dependencies on expat headers and sources
#16564: test to confirm behavior that regressed in python3.

Also add running of test_email_renamed to the email regrtest.  It contains
tests that the base email/tests/test_email.py does not, which I discovered
while trying to backport this test for confirmation of the behavior.
Keep IDLE from displaying spurious SystemExit tracebacks
when running scripts that terminated by raising SystemExit
(i.e. unittest and turtledemo).
Issue #17156: pygettext.py now correctly escapes non-ascii characters.
Minor cleanups.
Import shutil for restore_test_support_TESTFN().
Issue #6975: os.path.realpath() now correctly resolves multiple nested symlinks on POSIX platforms.
Issue #1470548: XMLGenerator now works with UTF-16 and UTF-32 encodings.
Issue #17149: Fix random.vonmisesvariate to always return results in [0, 2*math.pi].