upipe-avcdec: fix incorrect debug format strings

Use PRIu64 instead of %u/%d.
upipe-av: libavcodec/avcodec.h parsing

Export CFLAGS/AVFORMAT_CFLAGS and preproc local file that includes
<libavcodec/avcodec.h> instead of manually specifying libavcodec/avcodec.h
from AVFORMAT_CFLAGS.
Merge branch 'master' of git://github.com/cmassiot/upipe
Merge branch 'master' of git://github.com/cmassiot/upipe
Merge branch 'master' of http://git.notk.org/bencoh/upipe