[folks] Don't use deprecated string.ndup function.

[Travis Reitter <treitter src gnome org>]

commit c4ce8560e3d33ed93d814dec7829e81bb3fa3e7c
Author: Travis Reitter <travis reitter collabora co uk>
Date:   Mon Jan 31 09:36:29 2011 -0800

    Don't use deprecated string.ndup function.

 folks/persona.vala |    6 +++---
 1 files changed, 3 insertions(+), 3 deletions(-)
---
diff --git a/folks/persona.vala b/folks/persona.vala
index e680dc2..f502e73 100644
--- a/folks/persona.vala
+++ b/folks/persona.vala
@@ -232,10 +232,10 @@ public abstract class Folks.Persona : Object
       assert (backend_name_length != 0 && persona_store_id_length != 0);
 
       backend_name = Persona._unescape_uid_component (
-          uid.ndup (backend_name_length));
+          uid.substring (0, (long) backend_name_length));
       persona_store_id = Persona._unescape_uid_component (
-          ((string) ((char*) uid + backend_name_length + 1)).ndup (
-              persona_store_id_length));
+          ((string) ((char*) uid + backend_name_length + 1)).substring (0,
+              (long) persona_store_id_length));
       persona_id = Persona._unescape_uid_component (
           ((string) ((char*) uid + backend_name_length +
               persona_store_id_length + 2)));