By default, per-user directories (i.e. `/~username/`) are disabled in
Fedora's configuration of Apache. This commit introduces a new variable,
`apache_userdir`, which can be used to enable this feature. It should be
set to a string other than *disabled*, which is the path under users'
home directories that will be served, if it is accessible. Normally, the
value would be `public_html`.
