gfs2_edit: Print offsets of indirect pointers
    
    When printing indirect pointers gfs2_edit doesn't keep track of the
    location of the pointer within the indirect block and only prints an
    index for each non-zero pointer. Instead, store the offset of each
    non-zero pointer and print it when displaying indirect blocks, as it is
    done in interactive mode.
    
    Resolves: rhbz#1518938
    
    Signed-off-by: Andrew Price <anprice@redhat.com>