tests/test-chg.t

osx: add support for keeping mpkgs

This is a bit of a hack, but I don't really want to mount a dmg during
a test, and I don't see an option with hdiutil to take a dmg and spit
out a folder, so this is what we've got for now.

init repo

  $ hg init foo
  $ cd foo

ill-formed config

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