Modify the implementation of cursor caching to put cached cursors into a hash table. I think this means that putting a cursor into the cached state (by means of a cursor close), will take it off of the list of open cursors in the session, and insert it into the hashed table. Reopening a cursor will move it in the opposite direction. We'll need to audit that any code that walks the list of open cursors to make sure they don't need to account for the hash table. Session close, for example, will need to close cached cursors.

This is part of WT-1228.