This is one for the “read your changelog”-category. After upgrading to Ubuntu 13.10 you will notice that your Apache starts throwing 403 forbidden at you. The reason behind this is pretty simple, the Apache version changed to 2.4 and there are a lot of things to have a look at (http://httpd.apache.org/docs/current/upgrading.html).
In this particular case I assume you had your working dev-setup with something like:
The following part is what causes your problem. In Apache 2.4 the configuration has changed from
Order allow,deny Allow from all
Require all granted
Change this, restart and you are done =)