R1:854ed4ea53e3

Display link in commit ToC for directories

Summary:
They are present in the document so there is no reason to omit the links to
them.
Similar to D1412.

Test Plan: Display commit.

Reviewers: epriestley

Reviewed By: epriestley

CC: aran

Differential Revision: https://secure.phabricator.com/D1464