HAMMER kernel panic on git-clone

[Matthew Dillon]

    Bleh.  I just thought of another problem.  The kernel has no clue
    about PFS's.  I guess we have to do the cross-device link check in
    HAMMER anyway, so it can also check for attempts to link across PFS
    boundaries.

    Ok, let me fix this one, I have a patch set from the other work almost
    ready to go and I'll just add the appropriate code for the cross link
    check.

						-Matt