Merge from FreeBSD-cvsweb 2.0.0.
- cvsweb.conf-freebsd: Allow downloading a tarball of a project directory as well as a port directory.
- cvsweb.cgi, cvsweb.conf: Introduce optional output filter. [Requested by: Shigeyuki Fukushima <shige@FreeBSD.org>]
- cvsweb.cgi: Fix a bug where it produces wrong download links when cvsweb.cgi is placed right under the document root. [Reported by: Arnaud on EFnet]