Add seed values support for Query Builder order_by

(feature request #1987)
diff --git a/system/database/drivers/ibase/ibase_driver.php b/system/database/drivers/ibase/ibase_driver.php
index fc1c28f..02ec354 100644
--- a/system/database/drivers/ibase/ibase_driver.php
+++ b/system/database/drivers/ibase/ibase_driver.php
@@ -53,9 +53,9 @@
 	/**
 	 * ORDER BY random keyword
 	 *
-	 * @var	string
+	 * @var	array
 	 */
-	protected $_random_keyword = ' Random()';
+	protected $_random_keyword = array('RAND()', 'RAND()');
 
 	/**
 	 * IBase Transaction status flag