implement newOrNil, changes to stdlib

- newOrNil works like new, but sets the variable to nil
  if the heap allocation failed
- change stdlib to use newOrNil in openfile and openvolumeid
- changes to programs that use openvolumeid

progs/recover.pas

@@ -102,8 +102,8 @@ begin
 	count := PageMargin;
 
 	lastSlot := volumeTable[volid].part.dirSize - 1;
-	openvolumeid(volid);
-
+	openvolumeid(volid, error);
+		(* ignoring theoretically possible out-of-heap-space error *)
 	for i := 0 to lastSlot do
 	begin
 		getdirslot(volid, i, dirs, error);