Implement unsubscription in the Aphlict client.
Summary: Ref T5284. When an AphlictClient is closed, it will eventually be purged from the pool by the AphlictMaster. When this happens, also unsubscribe the purged client from all notifications, and send an unsubscribe command to the Aphlict server if possible.
Test Plan:
Verified the output of the Aphlict server (running in debug mode):
[Wed Jun 11 2014 23:21:31 GMT+0000 (UTC)] <FlashPolicy> Policy Request From ::ffff:192.168.1.1
[Wed Jun 11 2014 23:21:31 GMT+0000 (UTC)] <Listener/2> Connected from ::ffff:192.168.1.1
[Wed Jun 11 2014 23:21:31 GMT+0000 (UTC)] <Listener/2> Received data: {"command":"subscribe","data":["PHID-USER-cb5af6p4oepy5tlgqypi"]}
[Wed Jun 11 2014 23:21:31 GMT+0000 (UTC)] <Listener/2> Subscribed to: ["PHID-USER-cb5af6p4oepy5tlgqypi"]
[Wed Jun 11 2014 23:21:39 GMT+0000 (UTC)] <Listener/2> Received data: {"command":"subscribe","data":["PHID-TASK-l2dtbs5xrt2b7abgh5a6"]}
[Wed Jun 11 2014 23:21:39 GMT+0000 (UTC)] <Listener/2> Subscribed to: ["PHID-TASK-l2dtbs5xrt2b7abgh5a6"]
[Wed Jun 11 2014 23:21:57 GMT+0000 (UTC)] <Listener/2> Received data: {"command":"unsubscribe","data":["PHID-TASK-l2dtbs5xrt2b7abgh5a6"]}
[Wed Jun 11 2014 23:21:57 GMT+0000 (UTC)] <Listener/2> Unsubscribed from: ["PHID-TASK-l2dtbs5xrt2b7abgh5a6"]Reviewers: #blessed_reviewers, epriestley
Reviewed By: #blessed_reviewers, epriestley
Subscribers: epriestley, Korvin
Maniphest Tasks: T5284
Differential Revision: https://secure.phabricator.com/D9492