lavf/oggenc: use meaningful error codes

Signed-off-by: Lukasz Marek <lukasz.m.luki2@gmail.com>
Changelog: Add libpostproc visualization

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
doc/APIchanges: fill in hashes and dates

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
RELEASE_NOTES: update for 2.5

If you spot something missing wrong or improvable, do not hesitate
to push fixes

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