The algorithm for finding the block group descriptor blocks for the 
future on-line resizable ext2/3 format change got out of sync with 
what was actually shipped in e2fsprogs 1.30.  (And what is in e2fsprogs
1.30 is better since it avoids a free block fragmentation at the
beginning of the block group.)  This change is safe, since no one is 
actually using the new meta_bg block group layout just yet.