avconv: Report the codec and the encoder separately

Bug-Id: 694
Merge commit '39ec5e1cf8444f827c42effb76e5694e091bbff3'

* commit '39ec5e1cf8444f827c42effb76e5694e091bbff3':
  avconv: Report the codec and the encoder separately

Merged-by: Michael Niedermayer <michaelni@gmx.at>
Fix some fate filter tests with --target-path.
Fix rc_max_rate documentation.

The mpegvideo decoder sets rc_max_rate since 25b7aa98.