tests/test-dirstate-race2.t

tests: don't run couple of tests related to extensions loading with chg

The couple of files test extensions loading and debugging that. It sets
`devel.debug.extensions` to True to do that.
Either we have to restart chg if this config is set or just don't run these
tests on chg. I tried the first way by adding the config option to chgserver.py
list of config subsections but that does not seem to work.

Checking the size/permissions/file-type of files stored in the
dirstate after an update where the files are changed concurrently
outside of hg's control.

  $ hg init repo
  $ cd repo
  $ echo a > a
  $ hg commit -qAm _
  $ echo aa > a
  $ hg commit -m _

  $ hg debugdirstate --no-dates
  n 644          3 (set  |unset)               a (re)

  $ cat >> $TESTTMP/dirstaterace.py << EOF
  > from mercurial import (
  >     extensions,
  >     merge,
  > )
  > def extsetup(ui):
  >     extensions.wrapfunction(merge, 'applyupdates', wrap)
  > def wrap(orig, *args, **kwargs):
  >     res = orig(*args, **kwargs)
  >     with open("a", "w"):
  >         pass # just truncate the file
  >     return res
  > EOF

Do an update where file 'a' is changed between hg writing it to disk
and hg writing the dirstate. The dirstate is correct nonetheless, and
so hg status correctly shows a as clean.

  $ hg up -r 0 --config extensions.race=$TESTTMP/dirstaterace.py
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ hg debugdirstate --no-dates
  n 644          2 (set  |unset)               a (re)
  $ echo a > a; hg status; hg diff