dm-3.15-fixes-3

A dm-cache stable fix to split discards on cache block boundaries
because dm-cache cannot yet handle discards that span cache blocks.

Really fix a dm-mpath LOCKDEP warning that was introduced in -rc1.

Add a 'no_space_timeout' control to dm-thinp to restore the ability to
queue IO indefinitely when no data space is available.  This fixes a
change in behavior that was introduced in -rc6 where the timeout
couldn't be disabled.
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