syslog-ng: New package

syslog-ng is an enhanced log daemon, supporting a wide range of input
and output methods: syslog, unstructured text, queueing, SQL & NoSQL.

[Thomas:
 - Rewrap Config.in.help text
 - Pass --pidfile option when starting syslog-ng so that its PID file
   is created in /var/run/syslog-ng.pid, which allows
   start-stop-daemon to actually stop syslog-ng. Without this,
   S01logging was not able to stop syslog-ng.
 - Pass the executable path at stop time in S01logging, so that
   start-stop-daemon can check we're not incorrectly stopping
   something completely different.
 - Add busybox as a dependency of syslog-ng if busybox is enabled,
   since we want to override Busybox's S01logging init script.
 - Simplify the python condition, since python and python3 are
   mutually exclusive.
 - Rewrap the comment above SYSLOG_NG_FIXUP_CONFIG.]

Signed-off-by: Chris Packham <judge.packham@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>