Markup editor doesn't work nicely with IE8's "Find In This Page" feature

The Confluence Wiki markup editor grabs focus from the IE8 Find in this page toolbar after it highlights matching text, resulting in the user overwriting their content if they keep typing.

To reproduce:

1. Edit a page
2. Go into Wiki Markup mode if not already
3. Add content, e.g. "Hello World"
4. Hit CTRL+F to bring up IE's Find toolbar
5. Start typing "Hello". IE will match text and select it
6. As you keep typing, the editor will grab focus back and you will start over-writing your content