title: ng-xi18n script is failing as it is inspecting scss / sass files
body: <p>getting started with angular2s rc6 i18n, I want to run the ng-xi18n script to extract the corresponding i18n attributes for further processing.</p>
  
  <p>However the script fails with a message like</p>
  
  <pre><code>/project ❯❯❯ npm run extract                                                                                
  
  &gt; test.com@0.0.1 extract C:\project
  &gt; ng-xi18n
  
  Error: Compilation failed. Resource file not found: C:/project/src/styles/colors
      at Object.resourceLoader.get (C:\project\node_modules\@angular\compiler-cli\src\extract_i18n.js:127:27)
      at DirectiveNormalizer._fetch (C:\project\node_modules\@angular\compiler\bundles\compiler.umd.js:13450:45)
      at C:\project\node_modules\@angular\compiler\bundles\compiler.umd.js:13552:55
      at Array.map (native)
      at DirectiveNormalizer._loadMissingExternalStylesheets (C:\project\node_modules\@angular\compiler\bundles\compiler.umd.js:13552:16)
      at C:\project\node_modules\@angular\compiler\bundles\compiler.umd.js:13555:28
      at process._tickCallback (node.js:382:9)
      at Function.Module.runMain (module.js:433:11)
      at startup (node.js:141:18)
      at node.js:977:3
  TypeError: Cannot read property 'write' of undefined
      at C:\project\node_modules\@angular\compiler-cli\src\extract_i18n.js:34:46
      at process._tickCallback (node.js:382:9)
      at Function.Module.runMain (module.js:433:11)
      at startup (node.js:141:18)
      at node.js:977:3
  Extraction failed
  </code></pre>
  
  <p>Obviously, the script cannot find the file C:/project/src/styles/colors, which is perfectly true, as this is a sass partial and therefore is named _colors and referenced in a components own sass file used in styleUrls:[]</p>
  
  <p>Can I restrict the script to only investigate specific files (like all *.ts) or Why is it investigating my stylesheets?</p>
  
  <p>If it is valid to investigate stylesheet files, it seems the script is not aware of sass partial syntax.</p>
  
  <p>I'm using webpack for bundling and processing my sass files reference in styleUrls:[] to be inlined in my resulting files. But this should not be an issue as ng-xi18n is running on source not bundled.</p>
  
  <p>Any hint is appreciated. Thx.</p>