Support for base_path directive

[joamag]

This directive should be able to be defined in a per location basis.
Each location may have it's own base_path.
Must use the dispatcher handler to do the resolution of the index file according to this base path.
The dispatcher handler may send the complete file (resolved) to the underlying handlers on_full_path handler.

Configuration

[location:php]
path = [.]*\.php$
base_path = /usr/local/viriatum
handler = php
index = index.html index.php