Step 1 of the Big Error Shift: make os.Error an interface and replace *os.Errors with os.Errors.

lib/template updated to use new setup; its clients also updated.

Step 2 will make os's error support internally much cleaner.

R=rsc
OCL=27586
CL=27586

test/chan/goroutines.go

@@ -21,7 +21,7 @@ func f(left, right chan int) {
 func main() {
 	var n = 10000;
 	if len(sys.Args) > 1 {
-		var err *os.Error;
+		var err os.Error;
 		n, err = strconv.Atoi(sys.Args[1]);
 		if err != nil {
 			print("bad arg\n");