Properly detect launchd

Asterisk was a little too pro-active in claiming that it found launchd. On
systems without launchd - such as FreeBSD - this resulted in certain items
in Asterisk that conflict with launchd to not be selectable, such as
res_timing_kqueue.

(closes issue ASTERISK-20749)
Reported by: Oleg Baranov



git-svn-id: http://svn.asterisk.org/svn/asterisk/branches/1.8@381847 f38db490-d61c-443f-a65b-d21fe96a405b