Add an alsa plugin to output IEC958 frames over S/PDIF

Add an alsa plugin to output IEC958 frames over S/PDIF

Original commit message from CVS:
* configure.ac:
* ext/Makefile.am:
* ext/alsaspdif/Makefile.am:
* ext/alsaspdif/alsaspdifsink.c: (alsaspdifsink_base_init),
(alsaspdifsink_class_init), (alsaspdifsink_init),
(alsaspdifsink_dispose), (alsaspdifsink_set_property),
(alsaspdifsink_get_property), (alsaspdifsink_provide_clock),
(alsaspdifsink_get_time), (alsaspdifsink_open),
(alsaspdifsink_close), (alsaspdifsink_find_pcm_device),
(alsaspdifsink_write_frame), (alsaspdifsink_event),
(alsaspdifsink_get_times), (alsaspdifsink_current_delay),
(generate_iec958_zero_frame), (alsaspdifsink_render),
(ignore_alsa_err), (alsaspdifsink_change_state), (plugin_init):
* ext/alsaspdif/alsaspdifsink.h:
Add an alsa plugin to output IEC958 frames over S/PDIF