Initial focus should be set to the first focusable element instead of the dialog element.

@jscholes: Placing focus on the close button is the correct behaviour if the dialog has an accessible name via aria-label or aria-labelledby, which every dialog should. So a screen reader will announce the name, the role of dialog, then the close button.

The focus priority should be as follows:

1. element with [autofocus]
2. first focusable element if it's in the beginning of the dialog (usually the close button)
3. first element