tests/test-chg.t

destutil: add the ability to specify a search space for rebase destination

In the 'hg pull --rebase', we don't want to pick a rebase destination unrelated
to the pull, we lay down basic infrastructure to allow such restriction on
stable (before 3.8 release) in this case. See issue 5214 for details.

Actual usage and test will be in the next patch.

init repo

  $ hg init foo
  $ cd foo

ill-formed config

  $ hg status
  $ echo '=brokenconfig' >> $HGRCPATH
  $ hg status
  hg: parse error at * (glob)
  [255]