Small modification to please Safari in xml mode (1.6rc4)

In 1.6rc4, in the css fonction of the ui object, we try to create a
div with the following markup $('<div class="ui-gen">')
With safari, when a document is served as application/xhtml+xml,
innerHTML wants valid XML markup, and so this fails.
Just closing the div ( $('<div class="ui-gen"></div>') ) is enought to
make it work wonderfully again...