synergy hook DLL will now restart itself if a client tries to

init() it while it's already running.  fixed an uninitialized
pointer bug in CServer and some cleanup-on-error code in
CMSWindowsPrimaryScreen.  also added timeout to read() on
IInputStream and a heartbeat sent by clients so the server
can disconnect clients that are dead but never reset the TCP
connection.  previously the server would keep these dead
clients around forever and if the user was locked on the
client screen for some reason then the server would have to
be rebooted (or the server would have to be killed via a
remote login).

client/CClient.cpp

@@ -13,6 +13,7 @@
 #include "CTimerThread.h"
 #include "XThread.h"
 #include "CLog.h"
+#include "CStopwatch.h"
 #include "TMethodJob.h"
 #include <memory>
 
@@ -301,23 +302,36 @@ CClient::runSession(void*)
 		m_compressMouse = false;
 
 		// handle messages from server
+		CStopwatch heartbeat;
 		for (;;) {
 			// if no input is pending then flush compressed mouse motion
 			if (input->getSize() == 0) {
 				flushCompressedMouse();
 			}
 
-			// wait for reply
+			// wait for a message
 			log((CLOG_DEBUG2 "waiting for message"));
 			UInt8 code[4];
-			UInt32 n = input->read(code, 4);
+			UInt32 n = input->read(code, 4, kHeartRate);
 
-			// verify we got an entire code
+			// check if server hungup
 			if (n == 0) {
 				log((CLOG_NOTE "server disconnected"));
-				// server hungup
 				break;
 			}
+
+			// check for time out
+			if (n == (UInt32)-1 || heartbeat.getTime() > kHeartRate) {
+				// send heartbeat
+				CProtocolUtil::writef(m_output, kMsgCNoop);
+				heartbeat.reset();
+				if (n == (UInt32)-1) {
+					// no message to process
+					continue;
+				}
+			}
+
+			// verify we got an entire code
 			if (n != 4) {
 				// client sent an incomplete message
 				log((CLOG_ERR "incomplete message from server"));
@@ -347,6 +361,10 @@ CClient::runSession(void*)
 			else if (memcmp(code, kMsgDKeyRepeat, 4) == 0) {
 				onKeyRepeat();
 			}
+			else if (memcmp(code, kMsgCNoop, 4) == 0) {
+				// accept and discard no-op
+				continue;
+			}
 			else if (memcmp(code, kMsgCEnter, 4) == 0) {
 				onEnter();
 			}