Absolute path used for _diff

I have gitit running behind an Apache reverse proxy, so the URLs appear as e.g. http://x.x.x.x/wiki/

This mostly works fine. I can navigate to page history e.g.: http://x.x.x.x/wiki/_history/Front%20Page

However on the history when I drag one revision onto another I get a 404 error, and the URL bar shows the following: http://x.x.x.x/_diff/Front%20Page?from=xxxx&to=xxxx

Manually inserting the /wiki/ back into the URL makes the diff display correctly.

Version:

```
gitit version 0.8.1 +plugins
Copyright (C) 2008 John MacFarlane
This is free software; see the source for copying conditions. There is no
warranty, not even for merchantability or fitness for a particular purpose.
```