dm thin: put cells on the stack of thin_bio_map

(motivated by Mikulas' feedback on dm-devel.. matches what Alasdair
already staged for v3.9)
Merge branch 'thin-dev' of git://github.com/jthornber/linux-2.6 into thin-dev
[dm-cache] add a comment for the bvec_merge fn
Merge remote-tracking branch 'ejt/thin-dev' into thin-dev
Merge branch 'thin-dev' of git://github.com/jthornber/linux-2.6 into thin-dev
hint_size should be 4 given these policies do make use of hints
dm cache metadata: clean up includes by introducing dm-cache-block-types.h

Enables dm-cache-metadata.c to access policy methods
(e.g. dm_cache_policy_get_hint_size).

Also rename CACHE_POLICY_NAME_MAX to CACHE_POLICY_NAME_SIZE and re-use
in dm-cache-metadata.c (eliminates duplication in dm-cache-metadata.h).
dm cache metadata: add policy hint_size awareness

If policy's hint_size is 0 the the hint array isn't initialized/used.

policy_hint_size is added to the superblock but it doesn't _need_ to be
(I added it for symmetry with other variable passing between methods).

Hopefully this work gets us a bit closer to supporting variable hint_size.
Merge remote branch 'origin/thin-dev' into thin-dev
Merge branch 'thin-dev' into all-caches
Merge branch 'all-caches' of github.com:jthornber/linux-2.6 into all-caches