Asset pipeline — bundling plugin assets

I'm using rails from master and sprockets-2.0.0.beta.10. I've tried to use jQueryUI theme in a project but have no luck. What I've done:

— placed all assets in the /vendor/assets/stylesheets folder, so it looks like:

/stylesheets
--/ui-darkness
----/images
----jquery-ui-1.8.13.custom.css

— created index.css with the following content:

/*
*= require ./jquery-ui-1.8.13.custom
*= provide ./images
*/

and put it in the /ui-darkness folder.

— required in the application.css:

*= require_self
*= require ui-darkness
*= require_tree .

For now I've got index.css and jquery-ui-1.8.13.custom.css compiled into the application.css but other assets remained unreachable:

Started GET "/assets/images/ui-bg_glass_20_555555_1x400.png" for 127.0.0.1 at 2011-06-11 19:16:54 +0300  
Served asset /images/ui-bg_glass_20_555555_1x400.png - 404 Not Found  (4ms)  (pid 5822)