avformat/AVFormatContext: Move fields down to match the fork

avconv uses private and internal fields from libavformat, we thus must
match the layout even of the fields marked non public.
Otherwise ffmpegs libavformat could not be used as a dropin replacement
on debian/ubuntu

The current soname of libavformat was not part of any release nor are any
fields marked public moved thus in theory
no installed shared lib ABI breakage should occur. Still the need for this
change is unfortunate and chilling.
If you installed shared libs from a recent development version of libavformat
that is more recent than the last release. You probably want to check or rebuild
applications that linked to it.

minor versions of avformat & avdevice are bumped to allow detecting this
as both use the updated struct

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