Throw a useful error for deprecated use of Polymer.register

Fixes #210

gruntfile.js

@@ -38,7 +38,8 @@ module.exports = function(grunt) {
     "declaration/events.js",
     "declaration/properties.js",
     "declaration/attributes.js",
-    "declaration/polymer-element.js"
+    "declaration/polymer-element.js",
+    "deprecated.js"
   ].map(function(n) {
     return "src/" + n;
   });

polymer.js

@@ -31,7 +31,8 @@ var modules = [
   "declaration/events.js",
   "declaration/properties.js",
   "declaration/attributes.js",
-  "declaration/polymer-element.js"
+  "declaration/polymer-element.js",
+  "deprecated.js"
 ].map(function(n) {
   return "src/" + n;
 }));

src/deprecated.js

@@ -0,0 +1,14 @@
+/*
+ * Copyright 2013 The Polymer Authors. All rights reserved.
+ * Use of this source code is governed by a BSD-style
+ * license that can be found in the LICENSE file.
+ */
+
+// NOTE: put deprecated methods here that throw a useful error
+Polymer.register = function(context) {
+  if (context != window) {
+    // context is the <element> here, with a name attribute
+    var name = context.getAttribute('name');
+    throw new Error('Polymer.register is deprecated in declaration of ' + name + '. Please see http://www.polymer-project.org/getting-started.html');
+  }
+};