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/reclaim.pas

@@ -123,7 +123,8 @@ begin
 		freeAreaCount := 0;
 		lastUsed := 0;
 
-		openvolumeid(volid);
+		openvolumeid(volid, error);
+			(* ignoring theoretically possible out-of-heap-error *)
 		i := 0;
 		endSlot := volumeTable[volid].part.dirSize - 1;
 
@@ -308,7 +309,7 @@ begin
 		writeln('Volume ', volname, ' not found.')
 	else
 	begin
-		openvolumeid(volid);
+		openvolumeid(volid, error);
 
 		endSlot := volumeTable[volid].part.dirSize - 1;
 		extentSize := volumeTable[volid].part.extentSize;