title: Eclipse exclude php files from validation but not build
body: <p>I have a very simple use case. Eclipse Kepler with PDF. New project with PHP nature.</p>
  
  <p>One file at the root</p>
  
  <pre><code># test.php
  &lt;?php
  
  $fu = new Fu();
  $fu-&gt;bar();
  
  &amp;
  </code></pre>
  
  <p>One file in a directory</p>
  
  <pre><code># vendor/vendor.php
  &lt;?php
  
  class Fu {
      public function bar () {
  
      }
  }
  
  &amp;
  </code></pre>
  
  <p>Both files show an error in the Problems view. I need to exclude all files under vendor/ (recursively) from the Problems view, while keeping the code completion on objects defined under vendor/ (recursively).</p>
  
  <p>Desired result:</p>
  
  <ul>
  <li>code completion in test.php still works on Fu and all classes defined under vendor/</li>
  <li>the Problems view doesn't show any error or warning on files under vendor/</li>
  <li>the Problems view shows errors and warnings on other files as usual</li>
  <li>the Problems view doesn't depend on the selected element</li>
  </ul>
  
  <p>What I tried:</p>
  
  <ul>
  <li>removing vendor/ from the Build Path also removes all code completion on classes under vendor/</li>
  <li>Project > Properties > Validation > Enable project specific settings + PHP CodeSniffer Validator settings > Exclude Group > Folder: vendor doesn't do anything at all</li>
  </ul>