fix various typos

Signed-off-by: Lou Logan <lou@lrcd.com>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avcodec/libopenjpegenc: Add frame-threading capability

This gives a >50% speed up when encoding with libopenjpeg.

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>