Export SHOUTcast information (icy- headers)

[gjdfgh]

libavformat's http support does not appear to export these headers, which are needed to display metadata to the user when playing these streams. mplayer supports them.

These headers are dumped at the start of a streamed song, for example: "icy-genre:METAL, ROCK, ALTERNATIVE". Note that these can be updated mid-stream (e.g. on song change), and libavformat both needs to read that, and notify the application of it.

Useless required dump of ffplay output:

$ ffplay http://173.192.45.18:10200 
ffplay version 1.0.3 Copyright (c) 2003-2012 the FFmpeg developers
  built on Jan 24 2013 14:52:18 with gcc 4.7 (Debian 4.7.2-5)
  configuration: --prefix=/usr --extra-cflags='-g -O2 -fstack-protector --param=ssp-buffer-size=4 -Wformat -Werror=format-security ' --extra-ldflags='-Wl,-z,relro' --cc='ccache cc' --enable-shared --enable-libmp3lame --enable-gpl --enable-nonfree --enable-libvorbis --enable-pthreads --enable-libfaac --enable-libxvid --enable-postproc --enable-x11grab --enable-libgsm --enable-libtheora --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libx264 --enable-libspeex --enable-nonfree --disable-stripping --enable-libvpx --enable-libschroedinger --disable-encoder=libschroedinger --enable-version3 --enable-libopenjpeg --enable-librtmp --enable-avfilter --enable-libfreetype --enable-libvo-aacenc --disable-decoder=amrnb --enable-libvo-amrwbenc --enable-libaacplus --libdir=/usr/lib/i386-linux-gnu --disable-vda --enable-libbluray --enable-libcdio --enable-gnutls --enable-frei0r --enable-openssl --enable-libass --enable-libopus --enable-fontconfig --enable-libdc1394 --disable-altivec --disable-armv5te --disable  libavutil      51. 73.101 / 51. 73.101
  libavcodec     54. 59.100 / 54. 59.100
  libavformat    54. 29.104 / 54. 29.104
  libavdevice    54.  2.101 / 54.  2.101
  libavfilter     3. 17.100 /  3. 17.100
  libswscale      2.  1.101 /  2.  1.101
  libswresample   0. 15.100 /  0. 15.100
  libpostproc    52.  0.100 / 52.  0.100
[mp3 @ 0x80e0620] max_analyze_duration 5000000 reached at 5015510
[mp3 @ 0x80e0620] Estimating duration from bitrate, this may be inaccurate
Input #0, mp3, from 'http://173.192.45.18:10200':
  Duration: N/A, start: 0.000000, bitrate: 128 kb/s
    Stream #0:0: Audio: mp3, 44100 Hz, stereo, s16, 128 kb/s
   2.54 A-V:  0.000 fd=   0 aq=    2KB vq=    0KB sq=    0B f=0/0   

[Carl Eugen Hoyos]

Duplicate of ticket #716

For future reports: Please always test current git head and please provide ffmpeg output if applicable, only provide ffplay output if a problem is not reproducible with ffmpeg, see also ​http://ffmpeg.org/bugreports.html