This fixes error handling for BeOS, removing the need for some ifdefs.

AVERROR_ defines are moved to avcodec.h as they are needed in there as well. Feel free to move that to avutil/common.h.
Bumped up avcodec/format version numbers as though it's binary compatible we will want to rebuild apps as error values changed.
Please from now on use return AVERROR(EFOO) instead of the ugly return -EFOO in your code.
This also removes the need for berrno.h.

Originally committed as revision 7965 to svn://svn.ffmpeg.org/ffmpeg/trunk