more work on the elegant transcoder.
- fix problem where -debug builds were not staged (Fix issue #28).
- make packet stream index default to -1 until explicitly set.
- make muxer look for right stream by checking packet encoders if a
  stream index is not set.
- Fix a bug where we throw an exception if a codec id was
  AV_CODEC_ID_NONE on a decoder (can happen with some data streams).