Fix broken image links on demo

[hubdotcom]

http://phpthumb.sourceforge.net/demo/demo/phpThumb.demo.demo.php

1. http://phpthumb.sourceforge.net/demo/phpThumb.php?=&hash=dd319091134f863bf2edd258f8decaf6 (remove from demo?)
2. http://phpthumb.sourceforge.net/demo/phpThumb.php?src=http%3A%2F%2Fwww.silisoftware.com%2Fimages%2FSiliSoft.gif&w=100&hash=b2bc9058bc70a3f7aae22d7e254cf426 (need to add www.silisoftware.com to allowed external hosts)
3. http://phpthumb.sourceforge.net/demo/phpThumb.php?src=images%2FphpThumb.com.pdf&w=300&hash=12bebb8478b2cabd033456f229f89de3 (file missing http://phpthumb.sourceforge.net/demo/images/phpThumb.com.pdf)