fixed the following issues with detection of flow control mode

o the flow control contig frame thresh should be based on max array size
o it appears that the wakeup mechanism for the send thread, who sends
the flow control on/off messages was broken
o looking at full buffers isnt a perfect detection scheme compared to
the simpler approach of just checking to see if bytes are pending in
the socket before calling recv

src/ca/cac.cpp

@@ -143,6 +143,7 @@ cac::cac (
     initializingThreadsId ( epicsThreadGetIdSelf() ),
     initializingThreadsPriority ( epicsThreadGetPrioritySelf() ),
     maxRecvBytesTCP ( MAX_TCP ),
+    maxContigFrames ( contiguousMsgCountWhichTriggersFlowControl ),
     beaconAnomalyCount ( 0u ),
     iiuExistenceCount ( 0u )
 {
@@ -215,6 +216,11 @@ cac::cac (
         if ( ! this->tcpLargeRecvBufFreeList ) {
             throw std::bad_alloc ();
         }
+        unsigned bufsPerArray = this->maxRecvBytesTCP / comBuf::capacityBytes ();
+        if ( bufsPerArray > 1u ) {
+            maxContigFrames = bufsPerArray * 
+                contiguousMsgCountWhichTriggersFlowControl;
+        }
     }
     catch ( ... ) {
         osiSockRelease ();