Use a styled ul for the parentlinks.

On second thought, I've decided not to. Doing that would make ikiwiki less
usable in browsers like w3m that don't support styled uls. ikiwiki does use
styled uls for other things, such as the action bar, but displaying that as
a simple unstyled list in a simple browser works well and makes sense. For
parent links, it does not. --[[Joey]]
