module that is removed for testing "import" lines.  Originally deleted the
entry from sys.modules and then just let other code that needed it to import it
again.  Problem with this solution is that it lead to code that had already
imported the module in question to have their own reference to a new copy of
the module in question that new code couldn't reach.  This lead to a failure in
test_strptime since it monkey-patched the 'time' module it had a reference to
while _strptime had its own reference to another copy of 'time' from being
imported by test___all__ that it was using for a calculation.

Also moved the testing code out of the PthFile class and into the actual test
class.  This was to stop using 'assert' which is useless with a -O execution.