Edit toolbar - steal a little trick from DokuWiki: When you click a button

Edit toolbar - steal a little trick from DokuWiki: When you click a button
with no selection, the example text within the formatting, e.g. the "Link
title" in [[Link title]], is highlighted so that you can immediately type
over it.

Gecko only for now due to lack of testability under IE, if anyone wants to
hack it for IE, the code is at
http://wiki.splitbrain.org/lib/scripts/script.js

Note that they copied it from us first, so it's fair game ;-)