Fixed idle session processing

The current implementation of idle connection timeouts is not safe. The sessions
are handled in a way which is not thread-safe and the checking is done from
a non-polling thread.

With this change, the checks for the session timeouts are done in one of the
polling threads in a thread-safe manner only if at least one service has enabled
the timing out of idle client connections.

server/core/housekeeper.c

@@ -53,7 +53,7 @@ static HKTASK *tasks = NULL;
 static SPINLOCK tasklock = SPINLOCK_INIT;
 
 static int do_shutdown = 0;
-unsigned long hkheartbeat = 0;
+long hkheartbeat = 0; /*< One heartbeat is 100 milliseconds */
 
 static void hkthread(void *);