Added access to the "sqlMessage" of an error like does github:mysqljs/mysql

Author: williamdes

lib/packets/packet.js

@@ -713,6 +713,7 @@ Packet.prototype.asError = function(encoding) {
   err.code = ErrorCodeToName[errorCode];
   err.errno = errorCode;
   err.sqlState = sqlState;
+  err.sqlMessage = message;
   return err;
 };