Show correct pix_fmt for vp9 videos != AV_PIX_FMT_YUV420P.
Support libopenjpeg 2.x via libopenmj2.

Based on a patch by Marius Cirsta.

Fixes ticket #2016.
Autodetect jpg images.

Based on 2d3842f5 by Michael Niedermayer.

Fixes ticket #2541.