bprint: Include va_copy compat

Fixes build with MSVC and ICL.

Signed-off-by: Derek Buitenhuis <derek.buitenhuis@gmail.com>
lavd: Fix make checkheaders

Signed-off-by: James Almer <jamrial@gmail.com>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
lavu: fix grammar in doxy for av_frame_ref.

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