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/dumpdir.pas

@@ -14,8 +14,8 @@ var dirs:DirectorySlot;
     error:integer;
 begin
 	lastSlot := volumeTable[volid].part.dirSize - 1;
-	openvolumeid(volid);
-
+	openvolumeid(volid, error); (* we just ignore error here because
+		we should always have enough heap space *)
 	for i := 0 to lastSlot do
 	begin
 		getdirslot(volid, i, dirs, error);

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;

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);

progs/shell.pas

@@ -149,7 +149,7 @@ begin
 		count := PageMargin;
 
 		writeln('reading directory of ', DefaultVolume);
-		openvolumeid(volid);
+		openvolumeid(volid, error);
 		readdirfirst(volid, index, dirs, error);
 		while index > 0 do
 		begin

progs/xfer.pas

@@ -398,7 +398,7 @@ begin
 		writeln('Volume ', DefaultVolume, ' not found.')
 	else
 	begin
-		openvolumeid(volid);
+		openvolumeid(volid, error);
 		readdirfirst(volid, index, dirs, error);
 		while (index > 0) and (error = 0) do
 		begin