fsck.gfs2: Stop "undo" process when error data block is reached
    
    When fsck.gfs2 discovers a data block in error, it flags the error
    and especially in pass1, it tries to "undo" the block designations
    it previously marked in the blockmap. Before this patch, the "undo"
    functions didn't know when to stop. So it could "undo" designations
    in the blockmap that it hadn't "done" in the first place. With this
    patch, if an error is encountered while processing data blocks
    (not counting duplicate references--for example, blocks marked as
    'data' that are really dinodes which it hasn't gotten to yet) it
    saves off the block where the error occurred. Later, during the
    "undo" processing, it stops when it reaches the block that flagged
    the error.
    
    rhbz#902920