GreenletSet: add explicit block=False to kill() and killone() calls where we need async calls, since the default now is to block

update examples/dns_mass_resolve.py with regard to API change: Pool.spawn now blocks if there are not free slots

--HG--
rename : greentest/wsgi_test.py => greentest/test__pywsgi.py

make examples/wsgiserver.py to return the same replies as httpserver.py so that they can be tested with the same test