Service mod.: Proper(?) handling of return code 69

This adds "69" to the return codes from the status command that should be
considered as not running. At least "django-celery" uses this return code,
maybe others::

    /venv/bin/python /code/project/manage.py celeryctl status
    echo $? # 69 when not running.

A bit of googling let me to http://tldp.org/LDP/abs/html/exitcodes.html and
on a Ubuntu Server 12.10 I get::

    ~# cat /usr/include/sysexits.h | grep 69
    #define EX_UNAVAILABLE	69	/* service unavailable */

I'm not sure if the content of sysexits.h is the same on other OS'es.
Merge pull request #1872 from runekaagaard/devel

Service mod.: Proper(?) handling of return code 69