This is the fix for bugzilla 200883: gfs_fsck segfaults.
    The problem was that gfs_fsck was running out of memory
    for in-core bitmaps when run on very large file systems.
    For example, 45T requires about 11GB of memory.  This fix doesn't
    allow it to run, this just exits gracefully, tells them why,
    and how much additional memory is needed.