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/poll.c

@@ -35,6 +35,7 @@
 #include <maxconfig.h>
 #include <mysql.h>
 #include <resultset.h>
+#include <session.h>
 
 #define         PROFILE_POLL    0
 
@@ -705,6 +706,11 @@ poll_waitevents(void *arg)
             timeout_bias = 1;
         }
 
+        if (check_timeouts && hkheartbeat >= next_timeout_check)
+        {
+            process_idle_sessions();
+        }
+
         if (thread_data)
         {
             thread_data[thread_id].state = THREAD_ZPROCESSING;