gnbd can now multipath exported partitions, instead of just whole devices.
    Also, multipathd will now automagically monitor the gnbd devices correctly,
    and multipath will now automagically create multipath devices on top of the
    appropriate gnbds when they are imported, just like it does with other
    block devices when they are loaded.
    Fixes bug 196084, and a bunch of other ones which never got bugzillas.