* Add multiple yang support also for obsolete versions

* This means that files and datastores supporting modstate also looks for deleted or updated yang modules.
  * A stricter binding which gives error if loading outdated YANG file does not exist.
* Stricter yang checks: you cannot do get-config on datastores that have obsolete YANG
* Added xerr output parameter to `xmldb_get0()`

apps/backend/backend_main.c

@@ -946,6 +946,8 @@ main(int    argc,
 	if (startup_failsafe(h) < 0){
 	    goto done;
 	}
+	status = STARTUP_OK;
+	cbuf_reset(cbret); /* cbret contains error info */
     }
     
     /* Initiate the shared candidate. */