tests/test-dirstate-race.t

histedit: replaces patching logic by merges

The old and fragile patching logic is replaced by smart merges (as rebase and
graft do). This should prevents some conflicts and smoother human resolution.

For this purpose the "foldchanges" function is renamed to "applychanges" and
handle a single revision only.

  $ 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