debian: Update to 3.4.8

Signed-off-by: Gergely Nagy <algernon@madhouse-project.org>
debian: Add /var/log/error to logrotate

Closes: Debian#747020
Signed-off-by: Gergely Nagy <algernon@madhouse-project.org>
debian: Update the Homepage field

Point to http://www.syslog-ng.org/, now that we have relevant content
there.

Signed-off-by: Gergely Nagy <algernon@madhouse-project.org>