enhance evaluate (#3649)

lib/ast.js

@@ -618,7 +618,7 @@ var AST_PropAccess = DEFNODE("PropAccess", "expression property", {
     getProperty: function() {
         var p = this.property;
         if (p instanceof AST_Constant) {
-            return p.getValue();
+            return p.value;
         }
         if (p instanceof AST_UnaryPrefix
             && p.operator == "void"
@@ -824,9 +824,6 @@ var AST_This = DEFNODE("This", null, {
 
 var AST_Constant = DEFNODE("Constant", null, {
     $documentation: "Base class for all constants",
-    getValue: function() {
-        return this.value;
-    }
 });
 
 var AST_String = DEFNODE("String", "value quote", {