Coprocessor : Add combiner at Region server level.

End point coprocessors works on each region and send the result back to the client.If there is a scenario like aggregating the values based on some key patterns then we have to reduce all the results at the client side.
So if we can provide combiner( just like map/reduce) functionality at region server level then all region results can be reduced at region server and send the result to the client.This will reduce the network traffic as only single result will be sent by each region server.