Thanks to Felipe Contreras for the patch which this was based on.
Even though the MQ extension was only used in a single test
(test-pull-after-strip.t), I included it in the testutil. It shouldn't hurt
anything to have it enabled and not used, and saves us from having to deal
with enabling extensions in individual tests at all.
Similarly, this changeset results in the graphlog extension being enabled
for all tests, even though there were some that didn't use it before. This is
even less significant in Mercurial 2.3+, since in those versions, graphlog is
part of core, and is available even when the extension is disabled.
