[O-MPI devel] Registration Cache changes

[Galen M. Shipman]

Hi Gleb,

Tim and I have incorporated some of the changes you mentioned into a  
new rcache framework. Currently there is a single component in this  
framework, rcache_rb which is a registration cache based on a red- 
black tree  and uses an MRU list if the registration is not  
persistent. Note that each mpool now has it's own rcache instead of  
the btl's sharing an rcache. This has significantly simplified both  
the btls and the pml. Thanks for your input and please feel free to  
critique.

Galen