fate: run diff even if command fails

The diff may provide useful information even if the command was
unsuccessful.  The test is still treated as failed in this case.

Originally committed as revision 24353 to svn://svn.ffmpeg.org/ffmpeg/trunk

tests/fate-run.sh

@@ -95,7 +95,8 @@ seektest(){
 
 mkdir -p "$outdir"
 
-$command > "$outfile" 2>/dev/null || exit
+$command > "$outfile" 2>/dev/null
+err=$?
 
 if ! test -e "$ref"; then
     echo "reference file '$ref' not found"
@@ -108,4 +109,6 @@ case $cmp in
     stddev) stddev     "$ref" "$outfile" "$fuzz"    ;;
 esac
 
-test $? = 0 && rm $outfile
+cmperr=$?
+test $err = 0 && err=$cmperr
+test $err = 0 && rm $outfile