Fix some minor errors (DarkConsole warning, unstable Ferret sort)

Summary:
DarkConsole could warn when "Analyze Query Plans" was not active.

msort() is not stable, so Ferret results with similar relevance could be returned out-of-order.

Test Plan: Saw fewer traces and more-stable result ordering.

Differential Revision: https://secure.phabricator.com/D19236