dcb.c

dcb_write, if write failed, gwbuf wasn't freed.
mysql_backend.c 
	gw_MySQLWrite_backend, if dcb wasn'r in POLLING state then write was skpiped but gwbuf wasn't freed.
mysql_client.c
	gw_MySQLWrite_client, disabled the use of dcb_write because it returns different values than the code it replaced. Also removed erroneous call of gwbuf_consume.
mysql_common.c
	mysql_send_custom_error, removed erroneous call of gwbuf_free.

server/modules/protocol/mysql_common.c

@@ -805,7 +805,6 @@ mysql_send_custom_error (DCB *dcb, int packet_number, int in_affected_rows, cons
         // writing data in the Client buffer queue
         dcb->func.write(dcb, buf);
 
-        gwbuf_free(buf);
         return sizeof(mysql_packet_header) + mysql_payload_size;
 }