[ggevent] Stop quickly and cleanly on ppid change

This change should improve interaction with reloaders and ensure that
ports are not stuck open if the arbiter gets a hard kill signal or
otherwise exits during any graceful or non-graceful shutdown.
Forward-compatibility for gevent graceful shutdown

This commit closes the loop on fd6c712.

Aforementioned commit fixed observable problems in my testing with
gevent 1.0 release candidates but the explanation given at the time
was curiously bogus. It came from a misreading of pools and servers
as used in the ggevent worker.

With this change, both versions of gevent should support graceful
and non-graceful shutdown.
[ggevent] Don't die when logging requests

Some requests, such as websocket requests, may not have headers.