Normalize Phriction links when looking them up in remarkup
Summary: Fixes T10845.
Test Plan: Verified that [[ quack ]] and [[ QUACK ]] both work. Previously, the link had to exactly match the capitalization of the target.
Reviewers: chad
Reviewed By: chad
Maniphest Tasks: T10845
Differential Revision: https://secure.phabricator.com/D15777