title: Tycho downloads p2.indexes on every build
body: <p>I'm building an RCP and several other plug-ins with Maven &amp; Tycho. This works very fine, unless one issue:</p>
  
  <p>On every(!) build, Tycho loads <strike>all needed eclipse librarys, even when the where already downloaded 10 seconds ago. 
  Aren't they saved automatically in the local repository, or am I missing some configuration?</strike> all <code>p2.index</code>es. But this is also annoying. Can I turn this off, so that it'll only check once a week?</p>
  
  <pre><code>  &lt;properties&gt;
      &lt;tycho-version&gt;0.15.0&lt;/tycho-version&gt;
    &lt;/properties&gt;
  
    &lt;repositories&gt;
     &lt;repository&gt;
        &lt;id&gt;eclipse-indigo&lt;/id&gt;
        &lt;layout&gt;p2&lt;/layout&gt;
        &lt;url&gt;http://download.eclipse.org/releases/indigo&lt;/url&gt;
     &lt;/repository&gt;
    &lt;/repositories&gt;
  
    &lt;build&gt;
      &lt;plugins&gt;
        &lt;plugin&gt;
          &lt;groupId&gt;org.eclipse.tycho&lt;/groupId&gt;
          &lt;artifactId&gt;tycho-maven-plugin&lt;/artifactId&gt;
          &lt;version&gt;${tycho-version}&lt;/version&gt;
          &lt;extensions&gt;true&lt;/extensions&gt;
        &lt;/plugin&gt;
      &lt;/plugins&gt;
    &lt;/build&gt;
  </code></pre>