hghave: cache the result of gethgversion hghave --test-features calls it 90 times, each one calling hg --version which takes a tenth of a second on my workstation, adding up to about 10s win on test-hghave.t. Fixes https://bugs.debian.org/939756 Differential Revision: https://phab.mercurial-scm.org/D8092

clean: delete obsolete unlinking of .hg/graftstate The responsibility for clearing it is now in `cmdutil.clearunfinished()`, so we shouldn't have to unlink it in `hg.clean()`. Differential Revision: https://phab.mercurial-scm.org/D7992