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/include/mysql_client_server_protocol.h

@@ -299,6 +299,7 @@ typedef struct {
 
 void gw_mysql_close(MySQLProtocol **ptr);
 MySQLProtocol* mysql_protocol_init(DCB* dcb, int fd);
+void           mysql_protocol_done (DCB* dcb);
 MySQLProtocol *gw_mysql_init(MySQLProtocol *data);
 void gw_mysql_close(MySQLProtocol **ptr);
 int  gw_receive_backend_auth(MySQLProtocol *protocol);