Issue #191: Adapt bulk method signatures

Please comment already, but would like to see it merged after #204 
I think I've rewritten getAll() a few times over the course of the 107 stuff. So a few things I remember that you might want to consider. 

The first is that the mapping function is supposed to return an Iterable that is in the same order as the Iterable passed to it. There's nothing about the contract of CacheLoader.loadAll() that will gets this order correct. We won't notice anything wrong at the moment I think since all the bulk ops get converted to single-key operations by OnHeapStore. 

The other point is again about the contract of CacheLoader.loadAll(). It isn't particularly firm about whether the returned map needs to have all the keys in it, or that it cannot contain foriegn keys (ie. ones not present in the keys iteratble to loadAll())