xfs_repair: convert directory parsing to use libxfs structure

xfs_repair: convert directory parsing to use libxfs structure

It turns out that xfs_repair copies xfs_db in rolling it's own
opaque directory types for the different block formats. It has a
little comment about how they are "shared" with xfs_db. Shared by
copy and pasting, rather than a common header, it would appear.

Anyway, same problems, need to use format aware definitions and
abstractions from libxfs so that everything is parsed properly.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Ben Myers <bpm@sgi.com>
Signed-off-by: Ben Myers <bpm@sgi.com>