title: Issue in checkstyle configuration in IntelliJ Idea
body: <p>My objective is to implement Google's Java Style Checkstyle as stated in <a href="https://google-styleguide.googlecode.com/svn-history/r130/trunk/javaguide.html">https://google-styleguide.googlecode.com/svn-history/r130/trunk/javaguide.html</a> . </p>
  
  <p>In IntelliJ I have enabled Checkstyle plugin and try to point checkstyle xml (downloaded from <a href="https://github.com/checkstyle/checkstyle/blob/master/src/main/resources/google_checks.xml">https://github.com/checkstyle/checkstyle/blob/master/src/main/resources/google_checks.xml</a>).</p>
  
  <p>I got following exception:</p>
  
  <pre class="lang-none prettyprint-override"><code>Property 'fileExtensions' in module Checker does not exist
  </code></pre>
  
  <p>although this property is defined in the xml as</p>
  
  <pre class="lang-xml prettyprint-override"><code>&lt;property name="fileExtensions" value="java, properties, xml"/&gt;
  </code></pre>
  
  <p>Exception details:    </p>
  
  <pre class="lang-none prettyprint-override"><code>org.infernus.idea.checkstyle.exception.CheckStylePluginException:
  The CheckStyle rules file could not be loaded.
  Property 'fileExtensions' in module Checker does not exist, please check the documentation
  at org.infernus.idea.checkstyle.checker.CheckerFactory.blacklistAndShowMessage(CheckerFactory.java:248)
  at org.infernus.idea.checkstyle.checker.CheckerFactory.createChecker(CheckerFactory.java:202)
  </code></pre>