correction in a previously fixed test.

The hppa ubuntu box sometimes hangs forever in these tests.  My guess
is that the wait is failing for some reason.  Use WNOHANG, so we won't
wait until the buildbot kills the test suite.

I haven't been able to reproduce the failure, so I'm not sure if
this will help or not.  Hopefully, this change will cause the test
to fail, rather than hang.  That will be better since we will get
the rest of the test results.  It may also help us debug the real problem.

*** The reason this originally failed was because there were many
zombie children outstanding before rev 47158 cleaned them up.
There are still hangs in test_subprocess that need to be addressed,
but that will take more work.  This should close some holes.

be called at the end of each test that spawns children (perhaps it
should be called from regrtest instead?).  This will hopefully prevent
some of the unexplained failures in the buildbots (hppa and alpha)
during tests that spawn children.  The problems were not reproducible.
There were many zombies that remained at the end of several tests.
In the worst case, this shouldn't cause any more problems,
though it may not help either.  Time will tell.

is that the wait is failing for some reason.  Use WNOHANG, so we won't
wait until the buildbot kills the test suite.

I haven't been able to reproduce the failure, so I'm not sure if
this will help or not.  Hopefully, this change will cause the test
to fail, rather than hang.  That will be better since we will get
the rest of the test results.  It may also help us debug the real problem.

This was a fair amount of rework of the patch.  Refactored test_fork1 so it
could be reused by the new tests for wait3/4.  Also made them into new style
unittests (derive from unittest.TestCase).