HEADS UP - HAMMER work

[Matthew Dillon]

    I am adding some versioning infrastructure to HAMMER.  This will allow
    me to develop the 2.2 features (the new directory hash) in HEAD without
    messing up people currently using HAMMER on HEAD.

    There will be new ioctls and new hammer commands.  'hammer version <fs>'
    will retrieve the current version and with -v will display available
    versions.

    Also, HAMMER will refuse to mount HAMMER filesystems with versions it
    does not support.  Backwards compatibility is intended, but not
    forwards compatibility.

    'hammer version-upgrade <fs> ver#' can be used to upgrade a HAMMER
    filesystem.  Versions under development will require an additional
    'force' argument.  Currently version 2 is under development.  Once
    upgraded, a HAMMER filesystem may not be downgraded.

    DO NOT upgrade any production HAMMER filesystem to a WIP version (and
    currently the next version is a work-in-progress version so DO NOT
    upgrade!).  WIP versions are meant for developers who are helping test
    the filesystem and are likely to require numerous re-newfs's during the
    development cycle.  I will post when I need testing of development
    versions of HAMMER.

						-Matt