fixes #52, fields shadowing getters/setters or other fields

test/codegen/fields.dart

+// Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+library fields;
+
+init(x) {
+  print(x);
+  return x;
+}
+
+class Base {
+  var x = init('Base.x');
+}
+class Mixin1 {
+  var x = init('Mixin1.x');
+}
+class Mixin2 {
+  var x = init('Mixin2.x');
+}
+class Derived extends Base with Mixin1, Mixin2 {
+  var x = init('Derived.x');
+}
+
+// Private within the same library also needs this treatment.
+class _Base {
+  var x = init('_Base.x');
+}
+class _Mixin1 {
+  var _x = init('_Mixin1.x');
+}
+class _Mixin2 {
+  var _x = init('_Mixin2.x');
+}
+class _Derived extends _Base with _Mixin1, _Mixin2 {
+  var _x = init('_Derived.x');
+}
+
+
+main() {
+  print('Creating Derived');
+  print('Derived.x == ' + new Derived().x);
+  print('Creating _Derived');
+  print('_Derived.x == ' + new _Derived()._x);
+}