Fix some DB_cache-related issues

http://codeigniter.com/forums/viewthread/229610/
diff --git a/system/database/DB_driver.php b/system/database/DB_driver.php
index 4fcb6c6..1193b42 100644
--- a/system/database/DB_driver.php
+++ b/system/database/DB_driver.php
@@ -692,7 +692,7 @@
 			// resource ID won't be any good once we've cached the
 			// result object, so we'll have to compile the data
 			// and save it)
-			$CR = new CI_DB_result();
+			$CR = new CI_DB_result($this);
 			$CR->result_object	= $RES->result_object();
 			$CR->result_array	= $RES->result_array();
 			$CR->num_rows		= $RES->num_rows();