How do I configure apache to allow me to see /files correctly in a subdirectory?

img_assist inserts image links as /files/images/img.jpg, and this works ok if I install drupal to /var/www, but not if I use /var/www/example.

I assume that apache is configured to use /var/www as root folder, so how do I tell apache that /var/www/example is also a root folder for my test site?