rpc: add benchmark for async rpc calls Also makes sync benchmark concurrent.
rpc: add benchmark for async rpc calls
Also makes sync benchmark concurrent.

R=r, rsc
CC=golang-dev
http://codereview.appspot.com/4911043

Committer: Russ Cox <5ad239cb8a44f659eaaee0aa1ea5b94947abe557@golang.org>

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