more care around generated names, fixes #60 #82 and #97

test/codegen/names.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.
 
-import 'html_input_b.dart';
-import 'html_input_c.dart';
+var exports = 42;
+
+class Foo {
+  _foo() => 123;
+}
+
+_foo() => 456;
 
 main() {
-  print('fib(${x} + ${y}) = ');
-  print('  ... ${fib(x + y)}');
+  print(exports);
+  print(new Foo()._foo());
+  print(_foo());
 }