Import linux/gfs2_ondisk.h
    
    Give gfs2-utils its own copy of gfs2_ondisk.h. This allows us to always
    support the latest ondisk structures and obsoletes a lot of #ifdef
    GFS2_HAS_<FEATURE> blocks and configure.ac checks.
    
    Provide the kernel int typedefs that gfs2_ondisk.h uses with our own
    linux/types.h, which uses standard userspace types but keeps the bitwise
    attribute tags that sparse uses.
    
    Remove a bunch of unnecessary #include statements in the utils so that
    linux/gfs2_ondisk.h is never included and (our) linux/types.h is only
    ever included in libgfs2.h.
    
    Signed-off-by: Andrew Price <anprice@redhat.com>