Bug #468, http://bugs.skysql.com/show_bug.cgi?id=468, Query classifier accessed freed thread context. If parsing fails thd doesn't need to be freed because it holds correct information about command type.

session.c:session_setup_filters : fixed memory leak
hintparser.c: added token_free for HINT_TOKENs and fixed a few memory leaks.
mysql_client_server_protocol.h: added mysql_protocol_done which frees memory blocks pointed to by protocol members. Those can't be freed in dcb.c because dcb.c doesn't know about protocol's members.
mysql_backend.c:gw_backend_close: fixed memory leak
mysql_client.c: gw_client_close: fixed memory leak
mysql_common.c: added implementation of mysql_protocol_done
	:protocol_archive_srv_command: tried to fix memory leak. Some memory is still leaking according to valgrind. Removed use of uninitialized local variable len.
readwritesplit.c:execute_sescmd_in_backend: fixed a memory leak - visible only in DEBUG=Y build.

server/modules/protocol/mysql_backend.c

@@ -996,6 +996,8 @@ gw_backend_close(DCB *dcb)
 
         /** Send COM_QUIT to the backend being closed */
         mysql_send_com_quit(dcb, 0, quitbuf);
+        
+        mysql_protocol_done(dcb);
 
         if (session != NULL && session->state == SESSION_STATE_STOPPING)
         {