make some parse AST classes final

com.oracle.truffle.r.parser/src/com/oracle/truffle/r/parser/ast/For.java

@@ -4,7 +4,7 @@
  * http://www.gnu.org/licenses/gpl-2.0.html
  *
  * Copyright (c) 2012-2014, Purdue University
- * Copyright (c) 2013, 2015, Oracle and/or its affiliates
+ * Copyright (c) 2013, 2016, Oracle and/or its affiliates
  *
  * All rights reserved.
  */
@@ -14,7 +14,7 @@ import java.util.*;
 
 import com.oracle.truffle.api.source.*;
 
-public class For extends Loop {
+public final class For extends Loop {
 
     private final String variable;
     private final ASTNode range;

com.oracle.truffle.r.parser/src/com/oracle/truffle/r/parser/ast/Repeat.java

@@ -4,7 +4,7 @@
  * http://www.gnu.org/licenses/gpl-2.0.html
  *
  * Copyright (c) 2012-2014, Purdue University
- * Copyright (c) 2013, 2015, Oracle and/or its affiliates
+ * Copyright (c) 2013, 2016, Oracle and/or its affiliates
  *
  * All rights reserved.
  */
@@ -12,7 +12,7 @@ package com.oracle.truffle.r.parser.ast;
 
 import com.oracle.truffle.api.source.*;
 
-public class Repeat extends Loop {
+public final class Repeat extends Loop {
 
     Repeat(SourceSection source, ASTNode body) {
         super(source, body);

com.oracle.truffle.r.parser/src/com/oracle/truffle/r/parser/ast/While.java

@@ -4,7 +4,7 @@
  * http://www.gnu.org/licenses/gpl-2.0.html
  *
  * Copyright (c) 2012-2014, Purdue University
- * Copyright (c) 2013, 2015, Oracle and/or its affiliates
+ * Copyright (c) 2013, 2016, Oracle and/or its affiliates
  *
  * All rights reserved.
  */
@@ -14,7 +14,7 @@ import java.util.*;
 
 import com.oracle.truffle.api.source.*;
 
-public class While extends Loop {
+public final class While extends Loop {
 
     private final ASTNode condition;