Once Request Tracker 4 is installed on Debian 7, there is one more thing to do.
Small change in Apache configuration to make RT4 website to work.
First edit Apache configuration file:
root@hostname:~# vi /etc/apache2/sites-available/default
Then add to that file (at the end):
Include /etc/request-tracker4/apache2-modperl2.conf RedirectMatch ^/$ /rt </VirtualHost>