A Tiered Table spans multiple files/objects, each of which is accessed via a separate block handle (WT_BLOCK). 

Currently to find a block handle, we use a table of block handles that is part of the "current" block handle referenced from the block manager. I.e., bm->block->related[]

This is makes locking and coordination difficult. Looking up the block handle we need for a request requires that the current, unrelated handle stored in bm->block can't go away.

To eliminate this dependency we will move the list of handles being to the file into the block manager itself, so a lookup will only need the block manager (WT_BM).

Further details TBD.