Slight bug building ffmpeg-1.1.3 on OSX + patch to fix

Two instances of non-ascii characters have crept into file
doc/filters.texi which causes pod2man to error out and
break the build.

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
doc/ffmpeg: remove non ascii char

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