tests: add test coverage for lfdirstate invalidation of linear update f72d73937853 introduced a significant performance regression: All largefiles are marked 'normallookup' in lfdirstate by linear (or noop) updates and has to be rehashed by the next command. To avoid such regressions, keep an eye on the dirstate content after a plain 'hg up'.

test-subrepo-git: ignore global git config This was causing a test failure for people with company-wide settings. Still need a way to ignore local config.

tests/autodiff.py: explicitly only honor feature diffopts This test extension manages the opts it cares about on its own anyway.