fate: Force diff into text mode

On openbsd the exif-image-jpg test fails but diff treats the files as
binary due to some non ascii symbols in them. This should force it to
treat them as text, which should result in more informative output
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

tests/fate-run.sh

@@ -225,7 +225,7 @@ fi
 
 if test -e "$ref" || test $cmp = "oneline" ; then
     case $cmp in
-        diff)   diff -u -b "$ref" "$outfile"            >$cmpfile ;;
+        diff)   diff -u -a -b "$ref" "$outfile"         >$cmpfile ;;
         oneoff) oneoff     "$ref" "$outfile"            >$cmpfile ;;
         stddev) stddev     "$ref" "$outfile"            >$cmpfile ;;
         oneline)oneline    "$ref" "$outfile"            >$cmpfile ;;