* modules/codec/ffmpeg/encoder.c, modules/stream_out/transcode.c :

* modules/codec/ffmpeg/encoder.c, modules/stream_out/transcode.c :
  - new ffmpeg options available from the command-line : interleaved video,
    noise reduction, rate control parameters, i_quant_factor, trellis
    quantification, mpeg4 matrix, and thread count
  - portable functions to use ffmpeg multithreading capabilities on all
    platforms
  - hurry up mode now turns off rd and trellis, and also raises the noise
    reduction parameter (thus noise reduction is mandatory with hurry up)
  - if threads=1, no ffmpeg thread is launched, but the ffmpeg encoding
    will be done in a separate thread than the packetizer and decoder
  - fixed a bug with mp3 decoding and weird ffmpeg return code