Fix Mercurial commit history ordering
In D18769, I rewrote this from using the --branch flag (which is unsafe and does not function on branches named --config=x.y and such).
However, this rewrite accidentally changed the result order, which impacted Mercurial commit hisotry lists and graphs. Swap the order of the constraints so we get newest-to-oldest again, as expected.
Test Plan: Viewed a Mercurial repository's history graph, saw sensible chronology after the patch.
Reviewed By: amckinley
Differential Revision: https://secure.phabricator.com/D18817