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.
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