tests/test-dirstate-race.t

transaction: reorder unlinking .hg/journal and .hg/journal.backupfiles

After this reordering, absence of '.hg/journal' just before starting
new transaction means also absence of '.hg/journal.backupfiles'.

In this case, all temporary files for preceding transaction should be
completely unlinked, and HG_PENDING doesn't cause unintentional
reading stalled temporary files in.

Otherwise, 'repo.transaction()' raises exception with "run 'hg
recover' to clean up transaction" hint.

  $ hg init
  $ echo a > a
  $ hg add a
  $ hg commit -m test

Do we ever miss a sub-second change?:

  $ for i in 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20; do
  >     hg co -qC 0
  >     echo b > a
  >     hg st
  > done
  M a
  M a
  M a
  M a
  M a
  M a
  M a
  M a
  M a
  M a
  M a
  M a
  M a
  M a
  M a
  M a
  M a
  M a
  M a
  M a