libavutil/error.h.

Error code definitions and handling code belong to libavutil, where
they can be shared by all the libav* libraries.

See the thread:
Subject: [FFmpeg-devel] [PATCH] Move error codes definitions from lavc to lavu
Date: Sun, 19 Jul 2009 12:09:16 +0200

Originally committed as revision 22501 to svn://svn.ffmpeg.org/ffmpeg/trunk