xfs: online repair hard problems

This series tackles hard problems for online repair to solve.  Hard
problems are defined as ones that cannot be done without running afoul
of the regular xfs locking and synchronization rules.

We solve these problems by adding ability to freeze the filesystem to
perform a scrub operation, and then we add a couple more repair
functions to deal with incorrect fs summary counters and rebuild reverse
mapping btrees.
-----BEGIN PGP SIGNATURE-----
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=H8YQ
-----END PGP SIGNATURE-----