Do not trigger a possible custom autoloader, as it is irrelevant here

These were the last two calls of class_exists() without the $autoloader = FALSE argument.
diff --git a/system/core/Loader.php b/system/core/Loader.php
index d4e6323..6f90aec 100644
--- a/system/core/Loader.php
+++ b/system/core/Loader.php
@@ -658,7 +658,7 @@
 			return FALSE;
 		}
 
-		if ( ! class_exists('CI_Driver_Library'))
+		if ( ! class_exists('CI_Driver_Library', FALSE))
 		{
 			// We aren't instantiating an object here, just making the base class available
 			require BASEPATH.'libraries/Driver.php';