new widget "downloader"

[Jiao Lin]

Guys,

A new widget "downloader" was added to luban to make it easier to
handle download. You can use it to create a download link. A demo is
available at http://luban.danse.us/cgi-bin/aokuang/main.cgi?actor=downloader

When creating a downloader, you will need a label and a load action.
The routine that handles the load action must return a
luban.content.File.File object.

Please let me know if you find any problems when using it, or if you
have any comments.

You will need to update your luban installation from luban svn repo to use it.

Thanks,
Jiao