eventlet: after reaching max_requests, wait up to the graceful_timeout for
currently-running requests to complete.  fixes #511

Requests that do not complete within the graceful timeout are killed.
Merge pull request #532 from kevingessner/master

eventlet: after reaching max_requests, wait up to the graceful_timeout for currently-running requests to complete.  fixes #511
update THANKS
don't raise an error when we close the socket.

fix #537