Make HTC_Rx() return a distinct value for overflow/blast.
Teach vca_handover() to handle HTC_Rx() return status
Use HTC_Rx/vca_handover this way in all three acceptors.
Eliminate vca_pollsession()
Teach CNT_First() about HTC_Rx states.
Log which acceptor we use in shmlog



git-svn-id: http://www.varnish-cache.org/svn/trunk/varnish-cache@2084 d4fa192b-c00b-0410-8231-f00ffab90ce4