title: CGImageSourceCopyPropertiesAtIndex doesn't return keywords and other Photos.app fields
body: <p>In Photos.app on OS X I have specified a title, keywords and a description on a photo in my library. On iOS, I retrieved an PHAsset using the regular fetching methods. </p>
  
  <p>Then using <code>CGImageSourceCopyPropertiesAtIndex</code>, I fetched the metadata for the photo. The metadata is correct (it has all GPS and EXIF data), however it doesn't include any of those custom fields.</p>
  
  <p>The keywords and other fields are definitely on the device as I can search Photos.app on iOS by those fields and the photo is found.</p>
  
  <p>Is there another way to access these fields, or perhaps there is a bug with <code>CGImageSourceCopyPropertiesAtIndex</code>?</p>
  
  <pre><code>if let metadata = CGImageSourceCopyPropertiesAtIndex(imageSource, 0, nil) {
      print(metadata)
  }
  </code></pre>