tests/test-pull-update.t

merge: move almost all change/delete conflicts to resolve phase (BC) (API)

We have finally laid all the groundwork to make this happen.

The only change/delete conflicts that haven't been moved are .hgsubstate
conflicts. Those are trickier to deal with and well outside the scope of this
series.

We add comprehensive testing not just for the initial selections but also for
re-resolves and all possible dirstate transitions caused by merge tools. That
testing managed to shake out several bugs in the way we were handling dirstate
transitions.

The other test changes are because we now treat change/delete conflicts as
proper merges, and increment the 'merged' counter rather than the 'updated'
counter. I believe this is the right approach here.

For third-party extensions, if they're interacting with filemerge code they
might have to deal with an absentfilectx rather than a regular filectx.

Still to come:
- add a 'leave unresolved' option to merges
- change the default for non-interactive change/delete conflicts to be 'leave
  unresolved'
- add debug output to go alongside debug outputs for binary and symlink file
  merges

  $ hg init t
  $ cd t
  $ echo 1 > foo
  $ hg ci -Am m
  adding foo

  $ cd ..
  $ hg clone t tt
  updating to branch default
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ cd tt
  $ echo 1.1 > foo
  $ hg ci -Am m

  $ cd ../t
  $ echo 1.2 > foo
  $ hg ci -Am m

Should not update:

  $ hg pull -u ../tt
  pulling from ../tt
  searching for changes
  adding changesets
  adding manifests
  adding file changes
  added 1 changesets with 1 changes to 1 files (+1 heads)
  abort: not updating: not a linear update
  (merge or update --check to force update)
  [255]

  $ cd ../tt

Should not update:

  $ hg pull -u ../t
  pulling from ../t
  searching for changes
  adding changesets
  adding manifests
  adding file changes
  added 1 changesets with 1 changes to 1 files (+1 heads)
  abort: not updating: not a linear update
  (merge or update --check to force update)
  [255]

  $ HGMERGE=true hg merge
  merging foo
  0 files updated, 1 files merged, 0 files removed, 0 files unresolved
  (branch merge, don't forget to commit)
  $ hg ci -mm

  $ cd ../t

Should work:

  $ hg pull -u ../tt
  pulling from ../tt
  searching for changes
  adding changesets
  adding manifests
  adding file changes
  added 1 changesets with 1 changes to 1 files (-1 heads)
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved

  $ cd ..