Add optional alsa support

Alsa is usefull on embedded devices with few available
libraries, like some set top box, nas or similar.
Compile it with -DALSA and -lasound options
(Makefile.alsa provide an example)
Fix duplicate stuff_buffer call on alsa implementation
Abstract audio device related code

All the audio related code was removed from hairtunes sources
and moved out to external drivers.
There is an include file audio.h that define all the base audio
apis and the "hardware dependent" code inside audio_alsa.c and
audio_ao.c
Fix audio device lost in initialization (with libao)
Fix hairtunes still bootup if alsa initialization fail
Handle snd_pcm_recover when system suspend audio (alsa)

When the buffer go in underrun and we don't fill the audio
buffer faster enough, the system suspend the audio stream.
With snd_pcm_recover we restart the stream when a new frame
come.
Added te ability to specify the ao driver, devicename and deviceid when using the shairport binary
Made perl-version of shairport compatible with Perl 5.8
Merge pull request #1 from Xento/master

Some improvements to shairport
Accedently added thrashbytes in RSA-Key again to perl version
Merge pull request #3 from Xento/master

next try
make sure we don't overflow on string processing, even if constants are changed
make install a bit more portable
New connection verbose logs were displaying the local IP not the remote one. Fixed.
Quote the path to hairtunes (required if the path contains spaces).
Merge remote branch 'billitch/master'
Merge remote branch 'skaman/master'