tests/test-merge8.t

dirstate-guard: remove the feature

The dirstate guard duplicated some of the logic already implemented in the
transaction (and now the changing_* context).

However the feature was incomplete, for example, living only in memory meant we
could not recover from the hardest crash. In addition this duplicated with the
transaction logic meant things could go out of sync or step on each other.

Removing the feature now that we no longer needs it seems the safest.

Test for changeset ba7c74081861
(update dirstate correctly for non-branchmerge updates)
  $ hg init a
  $ cd a
  $ echo a > a
  $ hg add a
  $ hg commit -m a
  $ cd ..
  $ hg clone a b
  updating to branch default
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ cd a
  $ hg mv a b
  $ hg commit -m move
  $ echo b >> b
  $ hg commit -m b
  $ cd ../b
  $ hg pull ../a
  pulling from ../a
  searching for changes
  adding changesets
  adding manifests
  adding file changes
  added 2 changesets with 2 changes to 1 files
  new changesets e3c9b40284e1:772b37f1ca37
  (run 'hg update' to get a working copy)
  $ hg update
  1 files updated, 0 files merged, 1 files removed, 0 files unresolved

  $ cd ..