Associate segmentation_map[] with reference frame, rather than
decoding instance. This fixes cases where the map would be free()'ed
on e.g. a size change in one thread, whereas the other thread was
still accessing it. Also, it fixes cases where threads overwrite data
that is still being referenced by the previous thread, who thinks that
it's part of the frame previously decoded by the next thread.

Overhead as reported by rbelf-size goes from 90860 to 20204.

It's never been touched or used in any way since it was added in 2003
and only works for PIX_FMT_PAL8, which makes me conclude that nobody's
ever used it.

It's used in lavf.

They are used in lavf.

It's used in lavf.

It's used in lavf.

It's used in lavf.

It's used in lavf.

It's used in lavf.

Specifically, ff_dv_frame_profile and ff_dv_codec_profile.

Specifically, ff_flac_parse_streaminfo, ff_flac_is_extradata_valid and
ff_flac_parse_block_header

Specifically, ff_mpeg4audio_sample_rates, ff_mpeg4audio_get_config and
ff_copy_pce_data

Specifically, ff_mpa_freq_tab, ff_mpa_bitrate_tab, ff_mpa_decode_header,
ff_mpegaudio_decode_header.

It's used in lavf.

Overhead as reported by rbelf-size goes from 40147 to 20877.

They are used in libavdevice.

It's used in libavdevice.

enable CODEC_CAP_DELAY to flush any remaining frames in the buffer.

Stop decoding when the FN_QUIT command is found so that a trailing seek table
isn't decoded as a normal frame.

decode all channels in the same call to avcodec_decode_audio3() so that
decoding will not stop after the first channel of the last frame.

Updated FATE reference. More valid audio is now decoded.

decode_subframe_lpc().

just set data_size to zero.