[sm disk] be very careful to ensure that get_nr_free() returns the
count of blocks that can really be allocated at this instant.
[space map] comment to clarify the semantics of get_nr_blocks.
[sm metadata] tweak to pass the extra parameter for sm_ll_insert and friends.
[sm common] allow for bitmap search to fail if we start part way through
simplify init_pmd a bit
[btree-remove] extra BUG_ON paranoia
remove some spurious debug printks
Merge branch 'master' into thin-dev
dm thin: cleanup style nits in __pool_find

I couldn't resist...
[dm-thin] It is _not_ invalid to have low_water_mark == zero.  I don't
know when this check crept in.
[sm checker] comment out the get_nr_free bug_on, it's not a big deal if these values differ.
update todo
[bufio] fix memory corruption - from Mikulas
Merge branch 'thin-dev' into thin-stable
[TODO] update
[bufio] move into persistent-data and tidy.
[block-manager] turn block locking on all the time
[block-manager, transaction-manager] dm_bm_unlock_move
Merge branch 'thin-dev' into thin-stable
[bufio] remove a couple of printks