ext/flac/: Support chain-based operation, should make flac-over-DAAP work (#340492).

ext/flac/: Support chain-based operation, should make flac-over-DAAP work (#340492).

Original commit message from CVS:
* ext/flac/Makefile.am:
* ext/flac/gstflacdec.c: (gst_flac_dec_init),
(gst_flac_dec_reset_decoders),
(gst_flac_dec_setup_seekable_decoder),
(gst_flac_dec_setup_stream_decoder), (gst_flac_dec_finalize),
(gst_flac_dec_metadata_callback),
(gst_flac_dec_metadata_callback_seekable),
(gst_flac_dec_metadata_callback_stream),
(gst_flac_dec_error_callback),
(gst_flac_dec_error_callback_seekable),
(gst_flac_dec_error_callback_stream), (gst_flac_dec_read_seekable),
(gst_flac_dec_read_stream), (gst_flac_dec_write),
(gst_flac_dec_write_seekable), (gst_flac_dec_write_stream),
(gst_flac_dec_loop), (gst_flac_dec_sink_event),
(gst_flac_dec_chain), (gst_flac_dec_convert_sink),
(gst_flac_dec_get_sink_query_types), (gst_flac_dec_sink_query),
(gst_flac_dec_get_src_query_types), (gst_flac_dec_src_query),
(gst_flac_dec_handle_seek_event), (gst_flac_dec_sink_activate),
(gst_flac_dec_sink_activate_push),
(gst_flac_dec_sink_activate_pull), (gst_flac_dec_change_state):
* ext/flac/gstflacdec.h:
Support chain-based operation, should make flac-over-DAAP
work (#340492).