rpc: add benchmarks
rpc: add benchmarks

On my mac:
mallocs per rpc round trip: 144
rpc.BenchmarkEndToEnd	   10000	    228244 ns/op

Room for improvement.

R=rsc
CC=golang-dev
http://codereview.appspot.com/4274058

glycerine/jeaten-go-arrayof-structof,sanjosh/sanjos100-tipc,rflanagan/reginaldflanagan-project1,npe9/noahevans-go9,webfd/go-zh,d0f/go-zh,bryanxu/go-zh,sanjosh/sanjos100-tipc,webfd/go-zh,Triskite/willstone-goclone,rdp/rogerpack2005-golang,mhennings/marcohennings-go,Triskite/willstone-goclone,d0f/go-zh,rflanagan/reginaldflanagan-project1,d0f/go-zh,d0f/go-zh,rflanagan/reginaldflanagan-project1,webfd/go-zh,d0f/go-zh,webfd/go-zh,glycerine/jeaten-go-arrayof-structof,Triskite/willstone-goclone,Triskite/willstone-goclone,mhennings/marcohennings-go,bryanxu/go-zh,npe9/noahevans-go9,d0f/go-zh,scirelli/scirelli-go,sanjosh/sanjos100-tipc,mhennings/marcohennings-go,mhennings/marcohennings-go,npe9/noahevans-go9,scirelli/scirelli-go,scirelli/scirelli-go,d0f/go-zh,glycerine/jeaten-go-arrayof-structof,rdp/rogerpack2005-golang,scirelli/scirelli-go,sanjosh/sanjos100-tipc,glycerine/jeaten-go-arrayof-structof,scirelli/scirelli-go,Triskite/willstone-goclone,scirelli/scirelli-go,npe9/noahevans-go9,rdp/rogerpack2005-golang,bryanxu/go-zh,d0f/go-zh,sanjosh/sanjos100-tipc,bryanxu/go-zh,bryanxu/go-zh,webfd/go-zh,glycerine/jeaten-go-arrayof-structof,rflanagan/reginaldflanagan-project1,rdp/rogerpack2005-golang,mhennings/marcohennings-go,rflanagan/reginaldflanagan-project1,npe9/noahevans-go9,mhennings/marcohennings-go,rflanagan/reginaldflanagan-project1,sanjosh/sanjos100-tipc,rdp/rogerpack2005-golang,mhennings/marcohennings-go,rdp/rogerpack2005-golang,glycerine/jeaten-go-arrayof-structof,npe9/noahevans-go9,rdp/rogerpack2005-golang,glycerine/jeaten-go-arrayof-structof,rdp/rogerpack2005-golang,Triskite/willstone-goclone,sanjosh/sanjos100-tipc,sanjosh/sanjos100-tipc,mhennings/marcohennings-go,bryanxu/go-zh,Triskite/willstone-goclone,Triskite/willstone-goclone,webfd/go-zh,bryanxu/go-zh,bryanxu/go-zh,rflanagan/reginaldflanagan-project1,webfd/go-zh,scirelli/scirelli-go,webfd/go-zh,glycerine/jeaten-go-arrayof-structof,scirelli/scirelli-go,npe9/noahevans-go9,rflanagan/reginaldflanagan-project1,npe9/noahevans-go9