Support any name for the home directory [8.1]

As reported by Macnana in Repointer la page d'index vers un nouveau YAcs (in French), it is quite difficult to install yacs in a fancy directory and to have the top-level home page points to it.

Therefore, if you install yacs in the directory /foo instead of the standard /yacs, then the URL http://server/foo will load the home page as expected, but http://server/ will report an error.

To fix this situation you had to set the YACS_HOME environment variable to the correct value (e.g., foo in our previous example). However, this solution is not easy to deploy at most Internet service providers.

In the new version a new file yacs.home has been introduced to serve the same purpose. Create this file manually, at the home directory of the server, and put in it the name of the yacs directory. The updated index.php will read it to locate the yacs instance to use.