User tours accessibility: Tabbing should go back into the pop-up

User tours generally do a good job of accessibilty and keyboard support. However, there is a problem with tab order.

Steps to reproduce:

1. Go to qa.moodle.net, and log in as manager.
2. Go to Site administration / Appearance / User tours.
3. Edit the properties on the Boost - administrator tour, to show to all roles.
4. Go to the site home page.
5. Click Next, to get to the second step of the tour, about the navigation.
6. Press Tab a few times.

Actual results: keyboard focus can only move around the active parts of the page - the contents of the pop-up, and thing or things being hilighted. This is good.

What is bad is that once keyboard focus has reached the Navigation icon, it gets stuck there. (If there was more than one thing being hilighted, it woudl cycle round them.)

Interestingly, Shift-Tab works, but then gets stuck in the dialogue, and never gets to the items being higlighted.

In addition, when the pop-up opens, focus is initially on the whole dialogue (is this so screen-readers work?) However, that means that when you press Tab once, you get to the close icon, and you have to Tab once or twice more to get to Next. That is not ideal.