do not sort the results of getaddrinfo() because the order is actually important here

pywsgi: if we failed to send the reply, change 'status' to socket error so that the logs mention the error

wsgiserver.py: rename 'hello_world' to 'application'; only start server if run as a script (so that it can also be run by another server)

gevent.signal: spawn Greenlet instead of raw greenlet; switch into the greenlet immediatelly when the signal handler is called

start() no longer raises an exception if Greenlet was already started. it also now does nothing if the greenlet already exited (previously it would schedule another switch)

Hub: after LoopExit was raised, it was possible to switch into dead Hub; fix it to re-enter loop.run() and then raise LoopExit in a loop