title: Error with Typescript / whatwg-fetch / webpack
body: <p>I'm trying to have a simple demo app working using Typescript and React, with webpack. When I try to add whatgw-fetch to retrieve data from a server, I get this error when running webpack :</p>
  
  <pre><code>error TS2307: Cannot find module 'whatwg-fetch'
  </code></pre>
  
  <p>The error is on the import line : </p>
  
  <pre><code>import * as Fetch from 'whatwg-fetch'
  </code></pre>
  
  <p>I did install the npm dependency and the typing for typescript</p>
  
  <pre><code>npm install --save whatwg-fetch
  typings install --global --save dt~whatwg-fetch
  </code></pre>
  
  <p>My webpack configuration is : </p>
  
  <pre><code>var HtmlWebpackPlugin = require('html-webpack-plugin');
  var HTMLWebpackPluginConfig = new HtmlWebpackPlugin({
      template: __dirname + '/app/index.html',
      filename: 'index.html',
      inject: 'body'
  });
  var path = require('path');
  module.exports = {
      entry: [
          path.resolve(__dirname, 'app/index.tsx')
      ],
      output: {
          path: __dirname + '/dist',
          filename: "index_bundle.js"
      },
      resolve: {
          // Add `.ts` and `.tsx` as a resolvable extension. 
          extensions: ['', '.webpack.js', '.web.js', '.ts', '.tsx', '.js']
      },
      module: {
          loaders: [
              {test: /\.tsx$/, exclude: /node_modules/, loader: "ts-loader"}
          ]
      },
      plugins: [HTMLWebpackPluginConfig]
  };
  </code></pre>
  
  <p>I don't see any error in my IDE (IntelliJ IDEA) and if I change the import to some module that actually is not there, I get a different error (<code>Module not found: Error: Cannot resolve module 'whatwg-fetcha' in C:\dev\[...]</code>), and my IDE tells me the import is not valid.</p>
  
  <p>The import for basic React works fine with an equivalent setting : </p>
  
  <pre><code>npm install --save react
  typings install --global --save dt~react
  import * as React from 'react'
  </code></pre>
  
  <p>Am I missing something ? </p>
  
  <p>Thanks for your help.</p>