"Tiered Manager" implies a manager that is tiered.  What we really mean is a manager for tiered storage.  So we're switching this term to "Tier Manager".  At the moment this is largely unimplemented, so the change will be pretty easy. 

In the long run, we expect this to be a set of threads that handle background work such as garbage collection, tier merges, etc.  It will probably be modeled on similar functionality in the LSM code.

This ticket will change the existing uses of "tiered manager" in the source code to "tier manager".  It will also update the Technical Design document for PM-2119 to match.