title: Split Editor: Go to Definition opens a new tab in the current split even if the target is already open in another split
body: <ul>
  <li>VSCode Version: 1.8.1</li>
  <li>OS Version: Ubuntu 16.04.1 LTS</li>
  </ul>
  
  <p>Steps to Reproduce:</p>
  
  <ol>
  <li>Split Editor</li>
  <li>Open <code>source1.js</code> with a function definition in the first split</li>
  <li>Open <code>unrelated.js</code> in the first split</li>
  <li>The active tab in the first split is <code>unrelated.js</code></li>
  <li>Open <code>source2.js</code> calling the function in the second split</li>
  <li>From the second split ctrl+click on the function name</li>
  <li><code>source1.js</code> is opened again in the second split</li>
  </ol>
  
  <p>I would like to jump to the <code>source1.js</code> opened in the first split.</p>
  
  <p>Note: if <code>source1.js</code> is the active tab in the first split it works as expected.</p>