make AVOptions default value field work.

Patch by Panagiotis Issaris % takis P issaris A uhasselt P be %
Original thread:
Date: Sep 8, 2006 3:22 PM
Subject: [Ffmpeg-devel] [PATCH 1/2] Enable usage of AVOption default value

Originally committed as revision 6224 to svn://svn.ffmpeg.org/ffmpeg/trunk