Fix for email parsing from Outlook clients.

Summary: D1239 got it mostly right, but some versions of Outlook apparently put a '> ' in front of the 'Original Message' marker, which the parser couln't grok.

Test Plan: Added a test case to the unit tests, applied the patch to my install and asked one of my heathen Outlook using colleagues to reply to a Conpherence post.

Reviewers: epriestley, Blessed Reviewers

Reviewed By: epriestley, Blessed Reviewers

Subscribers: epriestley, Korvin

Differential Revision: https://secure.phabricator.com/D8998