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.

server/include/dcb.h

@@ -176,6 +176,8 @@ typedef struct dcb {
 	GWBUF		*writeq;	/**< Write Data Queue */
 	SPINLOCK	delayqlock;	/**< Delay Backend Write Queue spinlock */
 	GWBUF		*delayq;	/**< Delay Backend Write Data Queue */
+	GWBUF           *dcb_readqueue; /**< read queue for storing incomplete reads */
+	SPINLOCK        dcb_readqlock;  /**< read/write access protection to read queue */
 	SPINLOCK	authlock;	/**< Generic Authorization spinlock */
 
 	DCBSTATS	stats;		/**< DCB related statistics */