fix compile warning in rtsp.c
don't use "let" in configure script

bash-ism snuck into a nominally POSIX-compliant script
do not restart syscalls on SIGUSR1

SIGUSR1 is used to interrupt calls and shut down cleanly.
player/rtp: move packet loss & resend messages to debug level 1

This avoids spamming long-term logs with not-very-useful messages, which
also has the entertaining side-effect of choking systemd's hairy
journal daemon. Yuck. Fixes #278.
debian initscript: fix variable names

were not consistent with the default/shairport cfg file
tinysvcmdns: catch NULL ifa_addrs
audio_pipe: fd should be static
Makefile: build incrementally, default to -O2

As suggested by Andrew Pangborn (@Corv)
add ability to block whilst running start/stop external commands
tinysvcmdns: don't spin violently on shutdown

Linux overwrites the timeout argument with the remaining time when
select() returns, so if you don't reset it it shrinks to nothing.
Replaced with nanosleep() as per POSIX.1.
rtp/rtsp: report control port so we actually get resent packets

Detection and fix thanks to @Nachtzuster.

This still doesn't allocate the ports very cleverly at all. The port
handling code needs to be rewritten to allocate either one or three
ports, and then timing sync code can be sorted out...
fix RTSP fix

Previous commit was broken due to my stupidity.
Merge branch 'master' of https://github.com/abrasive/shairport into 1.0-dev