title: Class android.support.v7.app.ActionBar.Callback has already been added to output. Please remove duplicate copies
body: <p>I am using Android Studio and Gradle. I have to problem from v7 ActionBar. I clean and build my project and that error :</p>
  <blockquote>
  <p>Error : Class android.support.v7.app.ActionBar.Callback has already been added to output. Please remove duplicate copies.</p>
  <p>Execution failed for task ':MobilOnay:dexDebug'. Could not call IncrementalTask.taskAction() on task ':MobilOnay:dexDebug'</p>
  </blockquote>
  <p><strong>build.gradle</strong></p>
  <pre><code>// Top-level build file where you can add configuration options common to all sub-projects/modules.
  buildscript {
      repositories {
          mavenCentral()
      }
      dependencies {
          classpath 'com.android.tools.build:gradle:0.6.3'
      }
  }
  </code></pre>
  <p><strong>setting.gradle</strong></p>
  <pre><code>include ':PageIndacator'
  include ':MyProject'
  </code></pre>
  <p><strong>MyProject/build.gradle</strong></p>
  <pre><code>apply plugin: 'android'
  
  dependencies {
      compile fileTree(dir: 'libs', include: '*.jar')
      compile project(':PageIndacator')
      compile 'com.android.support:appcompat-v7:18.0.+'
  }
  
  android {
      compileSdkVersion 19
      buildToolsVersion &quot;19.0.0&quot;
  
      sourceSets {
          main {
              manifest.srcFile 'AndroidManifest.xml'
              java.srcDirs = ['src']
              resources.srcDirs = ['src']
              aidl.srcDirs = ['src']
              renderscript.srcDirs = ['src']
              res.srcDirs = ['res']
              assets.srcDirs = ['assets']
          }
  
          // Move the tests to tests/java, tests/res, etc...
          instrumentTest.setRoot('tests')
  
          // Move the build types to build-types/&lt;type&gt;
          // For instance, build-types/debug/java, build-types/debug/AndroidManifest.xml, ...
          // This moves them out of them default location under src/&lt;type&gt;/... which would
          // conflict with src/ being used by the main source set.
          // Adding new build types or product flavors should be accompanied
          // by a similar customization.
          debug.setRoot('build-types/debug')
          release.setRoot('build-types/release')
      }
  }
  </code></pre>
  <p><strong>PagaIndacator/build.gradle</strong></p>
  <pre><code>apply plugin: 'android-library'
  
  dependencies {
      compile 'com.android.support:support-v4:18.0.+'
  }
  
  android {
      compileSdkVersion 18
      buildToolsVersion &quot;19.0.0&quot;
  
      sourceSets {
          main {
              manifest.srcFile 'AndroidManifest.xml'
              java.srcDirs = ['src']
              resources.srcDirs = ['src']
              aidl.srcDirs = ['src']
              renderscript.srcDirs = ['src']
              res.srcDirs = ['res']
              assets.srcDirs = ['assets']
          }
  
          // Move the tests to tests/java, tests/res, etc...
          instrumentTest.setRoot('tests')
  
          // Move the build types to build-types/&lt;type&gt;
          // For instance, build-types/debug/java, build-types/debug/AndroidManifest.xml, ...
          // This moves them out of them default location under src/&lt;type&gt;/... which would
          // conflict with src/ being used by the main source set.
          // Adding new build types or product flavors should be accompanied
          // by a similar customization.
          debug.setRoot('build-types/debug')
          release.setRoot('build-types/release')
      }
  }
  </code></pre>
  <p><strong>MyProject/libs</strong></p>
  <pre><code>android-support-v7-appcompat.jar
  </code></pre>
  <p><strong>PageIndacator/libs is Empty</strong></p>