Disable autoloader call from class_exists() occurences to improve performance

Note: The Driver libary tests seem to depend on that, so one occurence in CI_Loader is left until we resolve that.
diff --git a/system/libraries/Xmlrpcs.php b/system/libraries/Xmlrpcs.php
index d4524d2..d263d78 100644
--- a/system/libraries/Xmlrpcs.php
+++ b/system/libraries/Xmlrpcs.php
@@ -31,7 +31,7 @@
 	show_error('Your PHP installation does not support XML');
 }
 
-if ( ! class_exists('CI_Xmlrpc'))
+if ( ! class_exists('CI_Xmlrpc', FALSE))
 {
 	show_error('You must load the Xmlrpc class before loading the Xmlrpcs class in order to create a server.');
 }