Fix error for URL's that could mean several commits

Summary: Ref T13001, URLs that return multiple commits should show a list of those commits. Not sure if the actual list looks very pretty this way, but was wondering if this approach was vaguely correct.

Test Plan:

• Navigate to install/rPbd3c23
• User should see a list view providing links to install/rPbd3c2355e8e2b220ae5e3cbfe4a057c8088c6a38 and install/rPbd3c239d5aada68a31db5742bbb8ec099074a561

Reviewers: epriestley, #blessed_reviewers

Reviewed By: epriestley, #blessed_reviewers

Subscribers: Korvin

Maniphest Tasks: T13001

Differential Revision: https://secure.phabricator.com/D18816