Support relative paths on 3.3 Cordova in Android

Hi, this change adds support for opening app relative paths, which is required in Cordova 3.5.

```
  cordova.plugins.fileOpener2.open(
      fileEntry.toURL(),
      'application/pdf',
      {
        error : function(errorObj) {
          console.log('Error status: ' + errorObj.status + ' - Error message: ' + errorObj.message);
        },
        success : function () {
          console.log('file opened successfully');
        }
      }
    );
```