Php schema patch to update channel id's of past events.

Summary: Php schema patch to update channel id's of past events.

Test Plan: Having some proxy issues here due to which connection is timing out and bot is not able to log into IRC. Bot connects to IRC in my home though ! So I wasn't able to quite to test this by running storage upgrade.

Reviewers: epriestley

CC: aran, Korvin

Differential Revision: https://secure.phabricator.com/D5000