Complete fix candidate for #645, http://bugs.skysql.com/show_bug.cgi?id=645 and #648, http://bugs.skysql.com/show_bug.cgi?id=648

tee.c:closeSession removed unnecessary dcb_free, router/service closes all backend DCBs and the client DCB, and client DCB is the one that was tried to free in closeSession.
readwritesplit.c:routeQuery now handles untyped and typed GWBUFs. Untyped means that read buffer may consist of incomplete and multiple MySQL packets. Typed buffer always consists of a single MySQL packet (which can be split to many buffers inside GWBUF).
Fixed Coverity cases #84840 and #84841

server/include/dcb.h

@@ -129,6 +129,9 @@ typedef struct {
  */
 #define	GWPROTOCOL_VERSION	{1, 0, 0}
 
+#define DCBFD_CLOSED -1
+#define DCBFD_CLONED -2
+
 /**
  * The statitics gathered on a descriptor control block
  */