Bug #425, http://bugs.skysql.com/show_bug.cgi?id=425
mysqlk_client.c now assumes that mysql packets may arrive in separate pieces.
gw_read_client_event reads client data, and if packet is incomplete it is added to new dcb->dcb_readqueue. When next packet is combined with data in readqueue.

mysql_common.c:gw_MySQL_get_next_packet can now return mysql packet from read buffer although it would span multiple gwbuf buffers.