Add some graceful error / missing feature handling.
Add some graceful error / missing feature handling.

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