title: maven-cobertura-plugion does not show the sources
body: <p>When I generate a Cobertura report by running "mvn cobertura:cobertura" (or "mvn site") then a report is generated which shows the test coverage for my classes but when I click on a class then the message "Unable to locate de/ailis/foo/Bar.java. Have you specified the source directory?" is displayed. How can I fix this? I configured the plugin in the pom.xml like this:</p>
  
  <pre><code>&lt;reporting&gt;
    &lt;plugins&gt;
      &lt;plugin&gt;
        &lt;groupId&gt;org.codehaus.mojo&lt;/groupId&gt;
        &lt;artifactId&gt;cobertura-maven-plugin&lt;/artifactId&gt;
        &lt;version&gt;2.4&lt;/version&gt;
      &lt;/plugin&gt;
    &lt;/plugins&gt;
  &lt;/reporting&gt;
  </code></pre>
  
  <p>So how can I specify the source directory for this plugin (And why is that needed, maven always knows where the source are and obviously they are already used because otherwise I should get an empty report).</p>