Log Message:
Initial import of dansguardian, provided by David Ferlier in PR pkg/24279.

DansGuardian is a web content filtering proxy for Linux, FreeBSD, OpenBSD,
and Solaris. It relies on a proxy server, for all fetching.  The preferred
proxy is Squid, however, DansGuardian should work with any proxy server.

It filters using multiple methods, including:
  - URL and domain filtering
  - textual content filtering
  - PICS filtering
  - MIME-type filtering
  - file extension filtering
  - POST filtering
  - user filtering
  - client IP filtering
  - exception lists for most of the above