Update to wordpress 3.9.1.

Changes:
- A smoother media editing experience
- Improved visual editing - speed, accessibility, and mobile support
- Edit images easily - quicker access to crop and rotation tools, scale images
  directly in the editor
- Drag and drop your images right onto the editor
- Image gallery previews right in the editor
- Showcase music and clips with simple audio and video playlists
- Live widget and header image previews in the Customizer
- Stunning new theme browser

Version 3.9.1 fixes 34 bugs from 3.9.

More details on http://codex.wordpress.org/Version_3.9 and
http://codex.wordpress.org/Version_3.9.1

(morr)