Some remotes don't respond as expected to the test. Retune will give connection
refused, because the test is made too quickly, before the service is running.
Even if we delay the test it won't work because Retune crashes.
Since the false mdns advertisements are only seen on Airplay, we only do the
test there.
Added configure checks needed to detect missing functions on OSX
Added compat clock functions using clock_get_time on OSX
Added compat timer functions using clock_gettime and setitimer on OSX
Added byteswap functions on OSX
