Cbufp

First cut implementation of shared page for transferring the cbuf collect list. Does not yet handle synchronization of the page.
This all looks great.  A simple change to fix the problem completely.  Once the collection buffers are filled asynchronously, I believe this will automagically just work for the majority of cases.  However, we might want to omit the call to _collect in the case where there are already entries in the shared buffer.  This would enable streaming memory without any calls to the cbufmgr at all.