title: Adding support libraries v7, v13 with gradle is not working
body: <p>I'm trying to import both android support libraries. I'm trying to implent GoogleMaps AP2 into my Android Application. Therefore I need both libraries. I'm using AndroidStudio and Gradle.</p>
  
  <pre><code>dependencies {
      compile fileTree(dir: 'libs', include: ['*.jar'])
      apt "org.androidannotations:androidannotations:$AAVersion"
      compile "org.androidannotations:androidannotations-api:$AAVersion"
      compile 'com.android.support:appcompat-v7:21.0.+'
      // compile 'com.google.android.gms:play-services:6.1.+'
      compile "com.android.support:support-v13:18.0.+"
      compile "com.loopj.android:android-async-http:1.4.5"
      repositories {
          mavenCentral()
      }
      compile "com.github.chrisbanes.actionbarpulltorefresh:library:+"
      compile 'joda-time:joda-time:2.5'
  }
  </code></pre>
  
  <p>The error is:</p>
  
  <pre><code>Module version com.android.support:support-v13:18.0.0 depends on libraries but is not a library itself
  </code></pre>