Add test for pipelining over two-party RPC.
Add test for pipelining over two-party RPC.

ligzy/capnproto,bryce-gibson/capnproto,nagyistoce/capnproto,artillery/capnproto,vladon/capnproto,a-richardson/capnproto,vladon/capnproto,hntrmrrs/capnproto,bsn069/capnproto,mrdomino/capnproto,maurer/capnproto,nagyistoce/capnproto,a-richardson/capnproto,kamalmarhubi/capnproto,geofft/capnproto,maurer/capnproto,MarPiRK/capnproto,joliss/capnproto,bsn069/capnproto,rcrowder/capnproto,zarvox/capnproto,joliss/capnproto,artillery/capnproto,nagyistoce/capnproto,artillery/capnproto,mrdomino/capnproto,jparyani/capnproto,MarPiRK/capnproto,ligzy/capnproto,a-richardson/capnproto,geofft/capnproto,ligzy/capnproto,khklau/capnproto,mrdomino/capnproto,pjulien/capnproto,pjulien/capnproto,rcrowder/capnproto,mologie/capnproto,jparyani/capnproto,martindale/capnproto,bryce-gibson/capnproto,mologie/capnproto,rcrowder/capnproto,martindale/capnproto,johnkdoe/capnproto,MarPiRK/capnproto,kamalmarhubi/capnproto,ocdtrekkie/capnproto,mologie/capnproto,Fraser999/capnproto,Fraser999/capnproto,geofft/capnproto,khklau/capnproto,joliss/capnproto,bryce-gibson/capnproto,maurer/capnproto,johnkdoe/capnproto,modulexcite/capnproto,modulexcite/capnproto,johnkdoe/capnproto,zarvox/capnproto,bsn069/capnproto,khklau/capnproto,ocdtrekkie/capnproto,kamalmarhubi/capnproto,martindale/capnproto,zarvox/capnproto,hntrmrrs/capnproto,pjulien/capnproto,ocdtrekkie/capnproto,Fraser999/capnproto,hntrmrrs/capnproto,vladon/capnproto,modulexcite/capnproto,jparyani/capnproto