run-tests: cache hghave results
Spawning a process on Windows is expensive. I've got a version of
test-lfs-test-server.t locally which prints the http request/responses that
totals 819 lines, with 149 conditional lines, 11 #if tests, and 2 test cases.
It takes just under 1 minute with this change to run both cases, vs just over
2 minutes without this change. Worse, when I explored adding ui.debug to the
test, it takes 13 minutes due to all of the mismatches and retests, vs less than
1 minute with this change. Overall, the difference when running all tests is
negligible- 103 minutes with this change, vs 105 without when using -j9.
It also looks like an exit value of 2 from `hghave` is treated specially, but
there's nothing preventing 2 missing features from also using this value.
mercurial (__VERSION__) __CODENAME__; urgency=medium
* Automated build performed by upstream.
-- Mercurial Devel <mercurial-devel@mercurial-scm.org> __DATE__