Improve Private Storage detection. MCabber now correctly detects Private Storage support when receiving an item-not-found error (which doesn't mean the server has no support for P.S., but that it's empty). I've added a return value to the callback functions. For now the return value is only used for IQ error handling.

--- a/mcabber/src/events.h	Tue May 01 16:33:26 2007 +0200
+++ b/mcabber/src/events.h	Tue May 01 18:16:11 2007 +0200
@@ -23,7 +23,7 @@
   time_t ts_expire;
   guint8 type;
   gpointer data;
-  void (*callback)();
+  int (*callback)();
   xmlnode xmldata;
   char *desc;
 } eviqs;