update: check wc.dirty() before setting overwrite=True merge.update() was missing a few dirtiness checks from workingcontext, including subrepo cleanliness checks. Using wc.dirty() instead of one-off checks for various forms of dirtiness will be significantly safer.

tags: don't allow environment errors to be raised from _writetagscache See https://bitbucket.org/tortoisehg/thg/issue/719

help/config: replace docutils markup