Bugzilla 220622: backport GFS2 statfs() implementation to GFS1.
    
      There are few compromises made while porting GFS2 approach over, mostly
      to avoid on-disk structure changes. GFS2 allocates (number-of-nodes + 1)
      physical files into disk during mkfs time but GFS1 only has one extra
      space (the unused license file) for this purpose. We deviate from GFS2
      by writing the local per-node changes into a memory buffer.
    
      Doing a "df" on a quiet filesystem now results:
    
      dhcp145 (1 cpu HP): old df took 0.875 seconds, new df 0.008 second
      dhcp146 (4 cpus DELL): old df took 0.808 seconds, new df 0.006 second.