Fix links in home page.

Web site: url.php?url=http://www.phpMyAdmin.net/ => OK
Improve:  url.php?url=http://www.phpmyadmin.neti/home_page/improve.php => broken
Support:  url.php?url=http://www.phpmyadmin.net/home_page/support.php  => broken

As domain name are not case sensitive, this seems the simpler fix.
(other solution, fix index.php to use CamelCase names for all links)