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.

and loading them via the other, except for the special cases of this
Guido added to test_datetime.py for datetime module objects.  The new
test_xpickle.py tries all of pickletester's AbstractPickleTests in
both x-module ways.