Add version validation for LookupMap, also add unittest directly in LookupMap (take 2)

pkg/lookup_map/test/version_check_test.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 'dart:io';
+import 'dart:mirrors';
+import 'package:lookup_map/lookup_map.dart'; // accessed via mirrors;
+import 'package:test/test.dart';
+import 'package:yaml/yaml.dart';
+
+/// This dartdoc helps remove a warning for the unused import on [LookupMap].
+main() {
+  test('validate version number matches', () {
+    var pubspecPath = Platform.script.resolve('../pubspec.yaml').path;
+    var yaml = loadYaml(new File(pubspecPath).readAsStringSync());
+    var version1 = yaml['version'];
+    var library = currentMirrorSystem().findLibrary(#lookup_map);
+    var version2 = library.getField(new Symbol('_version')).reflectee;
+    expect(version1, version2);
+  });
+}