[thin] Fix race condition between producer and consumer threads due to
the bio_prison being used inaccurately.
[transaction-manager] Add spin lock to protect shadow table, so we can
support multiple mutators.
update todo
agk's latest changes
[thin] remove discard support for now
[block-manager] From Mike Snitzer.  Give unique names to kmem_caches.
Merge branch 'corruption' into thin-dev
update todo
[thin] remove the consumer work queue, and rename the producer to
plain old worker.
persistent-data: small tweaks of block manager slab cache code
dm thin: kzalloc the pool_c structure

pool_c's dm_target_callbacks must be zeroed.
[thin] call process_prepared_mapping directly if we're skipping block
zeroing.
[thin] Now that we're allowing reads to provision and break sharing we
should change the io_covers_block optimisation to io_overwrites_block.
[unit-tests] add space-map-test