tests/test-revert-unknown.t

dispatch: move part of callcatch to scmutil

Per discussion at 39149b6036e6 [1], we need "callcatch" in worker.py. Move
it to scmutil.py to avoid cycles.

Note that dispatch's callcatch handles some additional high-level exceptions
related to config parsing, and commands. Moving them to scmutil will make
scmutil depend on "commands" or require "_formatparse" and "_getsimilar"
(and "difflib") to be moved as well. In the worker use-case, it is forked
when config and commands are fully loaded. So it should not care about those
exceptions.

[1]: https://www.mercurial-scm.org/pipermail/mercurial-devel/2016-August/087116.html

  $ hg init
  $ touch unknown

  $ touch a
  $ hg add a
  $ hg ci -m "1"

  $ touch b
  $ hg add b
  $ hg ci -m "2"

Should show unknown

  $ hg status
  ? unknown
  $ hg revert -r 0 --all
  removing b

Should show unknown and b removed

  $ hg status
  R b
  ? unknown

Should show a and unknown

  $ ls
  a
  unknown