t/perf: correctly align non-ASCII descriptions in output

Change the test descriptions from being treated as binary blobs by
perl to being treated as UTF-8. This ensures that e.g. a test
description like "æ" is counted as 1 character, not 2.

I have WIP performance tests for non-ASCII grep patterns on another
topic that are affected by this.

Now instead of:

    $ ./run p0000-perf-lib-sanity.sh
    [...]
    0000.4: export a weird var                                    0.00(0.00+0.00)
    0000.5: éḿíẗ ńöń-ÁŚĆÍÍ ćḧáŕáćẗéŕś   0.00(0.00+0.00)
    0000.7: important variables available in subshells            0.00(0.00+0.00)
    [...]

We emit:

    [...]
    0000.4: export a weird var                                 0.00(0.00+0.00)
    0000.5: éḿíẗ ńöń-ÁŚĆÍÍ ćḧáŕáćẗéŕś                          0.00(0.00+0.00)
    0000.7: important variables available in subshells         0.00(0.00+0.00)
    [...]

Fixes code originally added in 342e9ef ("Introduce a performance
testing framework", 2012-02-17).

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: avar

t/perf/aggregate.perl

@@ -88,6 +88,7 @@ sub format_times {
 sub read_descr {
 	my $name = shift;
 	open my $fh, "<", $name or return "<error reading description>";
+	binmode $fh, ":utf8" or die "PANIC on binmode: $!";
 	my $line = <$fh>;
 	close $fh or die "cannot close $name";
 	chomp $line;
@@ -147,6 +148,8 @@ sub have_slash {
 my $totalwidth = 3*@dirs+$descrlen;
 $totalwidth += $_ for (@colwidth);
 
+binmode STDOUT, ":utf8" or die "PANIC on binmode: $!";
+
 printf "%-${descrlen}s", "Test";
 for my $i (0..$#dirs) {
 	my $d = $dirs[$i];

t/perf/p0000-perf-lib-sanity.sh

@@ -33,6 +33,8 @@ test_perf 'export a weird var' '
 	test_export bar
 '
 
+test_perf 'éḿíẗ ńöń-ÁŚĆÍÍ ćḧáŕáćẗéŕś' 'true'
+
 test_expect_success 'test_export works with weird vars' '
 	echo "$bar" &&
 	test "$bar" = "weird # variable"