Manifest for cached files

Manifest file for use with [manifesto](https://github.com/cyberdelia/manifesto) did not take into account files which are cached and hashed. In the manifest.appcache file only merged file was added. This commit fixes this.


Example
-----------

In my settings file I have this configuration: 

```python
PIPELINE_JS = {
    'mainjs': {
        'source_filenames': (
            'js/*.js',
        ),
        'output_filename': 'js/main.js',
    }
}

STATICFILES_STORAGE = 'pipeline.storage.PipelineCachedStorage'
```

In the appcache file I receive main.js but not main.4de15f5275da.js. This is fixed.