tests/test-merge8.t

subrepo: pull revisions on demand when archiving hg subrepos

Before, running 'hg archive -S' could result in

 abort: unknown revision '65903cebad86f1a84bd4f1134f62fa7dcb7a1c98'!

if a subrepo was missing completely or had missing changesets. Now,
the missing changesets will be pulled or cloned as appropriate.

This make Mercurial subrepos match Git subrepos which already took
care to fetch any missing commits before starting the archive.

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
  (run 'hg update' to get a working copy)
  $ hg update
  1 files updated, 0 files merged, 1 files removed, 0 files unresolved