fix "Expect: continue-100" support on python 3
fix "Expect: continue-100" support on python 3

only bytes should be passed to the socket.

fix #560

jamesblunt/gunicorn,MrKiven/gunicorn,elelianghh/gunicorn,prezi/gunicorn,keakon/gunicorn,jamesblunt/gunicorn,tejasmanohar/gunicorn,gtrdotmcs/gunicorn,gtrdotmcs/gunicorn,ephes/gunicorn,ccl0326/gunicorn,WSDC-NITWarangal/gunicorn,zhoucen/gunicorn,malept/gunicorn,malept/gunicorn,wong2/gunicorn,z-fork/gunicorn,prezi/gunicorn,wong2/gunicorn,1stvamp/gunicorn,1stvamp/gunicorn,wong2/gunicorn,prezi/gunicorn,mvaled/gunicorn,ccl0326/gunicorn,zhoucen/gunicorn,alex/gunicorn,mvaled/gunicorn,zhoucen/gunicorn,malept/gunicorn,mvaled/gunicorn,harrisonfeng/gunicorn,tempbottle/gunicorn,ammaraskar/gunicorn,jamesblunt/gunicorn,alex/gunicorn,alex/gunicorn,gtrdotmcs/gunicorn,ccl0326/gunicorn,beni55/gunicorn,GitHublong/gunicorn,1stvamp/gunicorn