title: an existing package by the same name with a confilcting signature is already installed
body: <p>Hi I am developing an application that your use is private and i prefer not to upload to Google play.</p>
  
  <p>When the app opens check if exist new updates in a server, if exist download the apk and then install</p>
  
  <pre><code>    Intent i = new Intent();
      i.setAction(Intent.ACTION_VIEW);
      i.setDataAndType(Uri.fromFile(new File(Environment.getExternalStorageDirectory() + "/ipacUpdates/ipac.apk")), "application/vnd.android.package-archive" );
  
      this.ctx.startActivity(i);
  </code></pre>
  
  <p>When the installation finishes shows this error</p>
  
  <p><code>an existing package by the same name with a confilcting signature is already installed</code></p>
  
  <p>Both apk builded with the same machine and tested on <code>avd emulator</code>.</p>
  
  <p>What can be happening?</p>