title: webpack 2.1.0-beta.25 error unknown property postLoaders
body: <p>webpack 2.1.0-beta.25 (at least beta 23+) throws the following error if I specify <code>postLoaders: []</code> in my webpack.config:</p>
  
  <p>(just the interesting bit):</p>
  
  <pre><code>configuration.module has an unknown property 'postLoaders'.
  </code></pre>
  
  <p>(the full stack):</p>
  
  <pre><code>23 09 2016 13:37:31.599:ERROR [preprocess]: Can not load "webpack"!
  WebpackOptionsValidationError: Invalid configuration object. Webpack has been initialised using a configuration object that does not match the API schema.
  - configuration.module has an unknown property 'postLoaders'. These properties are valid:
  object { exprContextCritical?, exprContextRecursive?, exprContextRegExp?, exprContextRequest?, loaders?, noParse?, rules?, unknownContextCritical?, unknownContextRecursive?, unknownContextRegExp?, unknownContextRequest?, wrappedContextCritical?, wrappedContextRecursive?, wrappedContextRegExp? }
  Options affecting the normal modules (`NormalModuleFactory`).
      at webpack (/Users/jared.youtsey/src/Quartz/Common/source/node_modules/webpack/lib/webpack.js:16:9)
      at new Plugin (/Users/jared.youtsey/src/Quartz/Common/source/node_modules/karma-webpack/lib/karma-webpack.js:63:18)
      at invoke (/Users/jared.youtsey/src/Quartz/Common/source/node_modules/di/lib/injector.js:75:15)
      at Array.instantiate (/Users/jared.youtsey/src/Quartz/Common/source/node_modules/di/lib/injector.js:59:20)
      at get (/Users/jared.youtsey/src/Quartz/Common/source/node_modules/di/lib/injector.js:48:43)
      at /Users/jared.youtsey/src/Quartz/Common/source/node_modules/di/lib/injector.js:71:14
      at Array.map (native)
      at Array.invoke (/Users/jared.youtsey/src/Quartz/Common/source/node_modules/di/lib/injector.js:70:31)
      at Injector.get (/Users/jared.youtsey/src/Quartz/Common/source/node_modules/di/lib/injector.js:48:43)
      at instantiatePreprocessor (/Users/jared.youtsey/src/Quartz/Common/source/node_modules/karma/lib/preprocessor.js:55:20)
      at Array.forEach (native)
      at createPreprocessor (/Users/jared.youtsey/src/Quartz/Common/source/node_modules/karma/lib/preprocessor.js:74:20)
      at Array.invoke (/Users/jared.youtsey/src/Quartz/Common/source/node_modules/di/lib/injector.js:75:15)
      at get (/Users/jared.youtsey/src/Quartz/Common/source/node_modules/di/lib/injector.js:48:43)
      at /Users/jared.youtsey/src/Quartz/Common/source/node_modules/di/lib/injector.js:71:14
      at Array.map (native)
  </code></pre>
  
  <p>My webpack.config:</p>
  
  <pre><code>process.env.npm_lifecycle_event = 'test';
  var webpack = require('webpack');
  var path = require('path');
  var NODE_MODULES = root("node_modules");
  
  function root(args) {
      args = Array.prototype.slice.call(arguments, 0);
      return path.join.apply(path, [__dirname].concat(args));
  }
  
  module.exports = {
      entry: {},
  
      resolve: {
          modules: [root(""), NODE_MODULES],
          extensions: [".ts", ".js", ".json", ".css", ".scss", ".html"]
      },
  
      module: {
          loaders: [
              {
                  test: /\.ts$/,
                  loader: "ts",
                  query: {
                      "ignoreDiagnostics": [
                          2403, // 2403 -&gt; Subsequent variable declarations
                          2300, // 2300 -&gt; Duplicate identifier
                          2374, // 2374 -&gt; Duplicate number index signature
                          2375, // 2375 -&gt; Duplicate string index signature
                          2502  // 2502 -&gt; Referenced directly or indirectly
                      ]
                  },
                  exclude: [/node_modules\/?!(@angular)/]
              },
  
              { test: /\.scss$/, loader: "null" },
              { test: /\.css$/, loader: "null" },
              { test: /\.html$/, loader: "raw" }
          ],
          postLoaders: [
              {
                  test: /\.(js|ts)$/,
                  include: [root("")],
                  loader: "istanbul-instrumenter-loader",
                  exclude: [/.+-spec\.ts$/, /\.e2e\.ts$/, NODE_MODULES]
              }
          ]
      }
  };
  </code></pre>
  
  <p>It appears that the documentation for loaders on the webpack site still references pre/postLoaders.  But either one, even if empty, will still generate this error.</p>
  
  <p>Has the schema changed?  Where should the postLoaders go, or, how should a postLoader be configured?</p>