iff: support IFF ILBM with byterun2 compression

[ami_stuff]

this was a format used by DeluxePaint for Atari ST

supported by recoil:

​http://recoil.sourceforge.net/

(search for "RECOIL_DecodeIff" in "recoil.c")

C:\>ffmpeg -i atari_neworld.iff  out.bmp
ffmpeg version N-78758-g5156578 Copyright (c) 2000-2016 the FFmpeg developers
  built with gcc 5.3.0 (GCC)
  configuration: --enable-gpl --enable-version3 --disable-w32threads --enable-av
isynth --enable-bzlib --enable-fontconfig --enable-frei0r --enable-gnutls --enab
le-iconv --enable-libass --enable-libbluray --enable-libbs2b --enable-libcaca --
enable-libdcadec --enable-libfreetype --enable-libgme --enable-libgsm --enable-l
ibilbc --enable-libmodplug --enable-libmp3lame --enable-libopencore-amrnb --enab
le-libopencore-amrwb --enable-libopenjpeg --enable-libopus --enable-librtmp --en
able-libschroedinger --enable-libsoxr --enable-libspeex --enable-libtheora --ena
ble-libtwolame --enable-libvidstab --enable-libvo-amrwbenc --enable-libvorbis --
enable-libvpx --enable-libwavpack --enable-libwebp --enable-libx264 --enable-lib
x265 --enable-libxavs --enable-libxvid --enable-libzimg --enable-lzma --enable-d
ecklink --enable-zlib
  libavutil      55. 19.100 / 55. 19.100
  libavcodec     57. 27.100 / 57. 27.100
  libavformat    57. 26.100 / 57. 26.100
  libavdevice    57.  0.101 / 57.  0.101
  libavfilter     6. 37.100 /  6. 37.100
  libswscale      4.  0.100 /  4.  0.100
  libswresample   2.  0.101 /  2.  0.101
  libpostproc    54.  0.100 / 54.  0.100
Input #0, iff, from 'atari_neworld.iff':
  Duration: N/A, bitrate: N/A
    Stream #0:0: Video: iff_ilbm (ILBM / 0x4D424C49), pal8, 320x200, SAR 9:10 DA
R 36:25, 90k tbr, 90k tbn, 90k tbc
[image2 @ 038f0bc0] Frame rate very high for a muxer not efficiently supporting
it.
Please consider specifying a lower framerate, a different muxer or -vsync 2
Output #0, image2, to 'out.bmp':
  Metadata:
    encoder         : Lavf57.26.100
    Stream #0:0: Video: bmp, pal8, 320x200 [SAR 9:10 DAR 36:25], q=2-31, 200 kb/
s, 90k fps, 90k tbn, 90k tbc
    Metadata:
      encoder         : Lavc57.27.100 bmp
Stream mapping:
  Stream #0:0 -> #0:0 (iff_ilbm (iff) -> bmp (native))
Press [q] to stop, [?] for help
[iff @ 038f0660] bitmap (compression 2, bpp 4, ham 0) is not implemented. Update
 your FFmpeg version to the newest one from Git. If the problem still occurs, it
 means that your file has a feature which has not been implemented.
[iff @ 038f0660] If you want to help, upload a sample of this file to ftp://uplo
ad.ffmpeg.org/incoming/ and contact the ffmpeg-devel mailing list. (ffmpeg-devel
@ffmpeg.org)
Error while decoding stream #0:0: Invalid data found when processing input
frame=    0 fps=0.0 q=0.0 Lsize=N/A time=00:00:00.00 bitrate=N/A speed=N/A
video:0kB audio:0kB subtitle:0kB other streams:0kB global headers:0kB muxing ove
rhead: unknown
Output file is empty, nothing was encoded (check -ss / -t / -frames parameters i
f used)
Conversion failed!

[ami_stuff]

​http://pulkomandy.tk/projects/GrafX2/ticket/38

[Elon Musk]

Fixed in 49633f9f7498499d63391eb1351de66a8f603060.