Revert:

Revert:
	r18826 | stefano | 2009-05-14 20:50:58 +0200 (Thu, 14 May 2009) | 2 lines
	Make av_set_string3() print a message in case of unknown option.

This change led to multiple identical error messages to be printed if an option
was not found.

Originally committed as revision 20172 to svn://svn.ffmpeg.org/ffmpeg/trunk