Improve Conpherence behavior for logged out users.

Summary:
There are two issues here I was trying to fix:

• Viewing /conpherence by logged out users on secure would generate an overheated query on ConpherenceThreadQuery secure has a ton of wacky threads with bogus names.
• When a user views a specific thread that they don't have permission to see, we attempt to fetch the thread's transactions before applying policy filtering. If the thread has more than 1000 comments, that query will also overheat instead of returning a policy exception.

I fixed the first problem, but started trying to fix the second by moving the transaction fetch to didFilterPage but it broke in strange ways so I gave up.

Also fix a dangling qsprintf update.

Test Plan: Loaded threads and the Conpherence homepage with and without logged in users.

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: Korvin

Differential Revision: https://secure.phabricator.com/D20375