Select correct link in file tree

Summary:
Clicking on a shielded file in file tree highlighted the previous one.
Also, menu bar is not fixed anymore.

Test Plan: D3355#d77999bc - scripts/celerity_mapper.php was highlighted.

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, Korvin

Differential Revision: https://secure.phabricator.com/D3806