tests/test-dirstate-race.t

clone: fix updaterev to update to latest branch changeset (issue4528)

Before this patch if clone --updaterev points to branch which head
on src repo wasnt in dest repo, clone updated dest repo to
default branch. After applying this patch, if changeset from
src repo pointing at given branch is not in dest repo, it searches
for changeset pointing for given branch locally in dest repo.

Lookup in destination repo:
  559: uprev = destrepo.lookup(update)
is wrapped by try/except block to preserve current behaviour when
given revset to -u is not found - it will not fail,but silently update
dest repo to head of default branch.

  $ 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