tests: extract extension configuration into a testutil library 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.