gitweb: Fix the author initials in blame for non-ASCII names

Change the @author_initials feature Jakub added in
v1.6.4-rc2-14-ga36817b to match non-ASCII author initials as intended.

The regexp Jakub added was intended to match
non-ASCII (/\b([[:upper:]])\B/g). But in Perl this doesn't actually
match non-ASCII upper-case characters unless the string being matched
against has the UTF8 flag.

So when we open a pipe to "git blame" we need to mark the file
descriptor we're opening as utf8 explicitly.

So as a result it abbreviates me to "AB" not "ÆAB", entirely because "Æ"
isn't /[[:upper:]]/ unless the string being matched against has the UTF8
flag.

Here's something that demonstrates the issue:

    #!/usr/bin/env perl
    use strict;
    use warnings;

    binmode STDOUT, ':utf8' if $ENV{UTF8};
    open my $fd, "-|", "git", "blame", "--incremental", "--", "Makefile" or die "Can't open: $!";
    binmode $fd, ":utf8" if $ENV{UTF8};
    while (my $line = <$fd>) {
    	next unless my ($author) = $line =~ /^author (.*)/;
    	my @author_initials = ($author =~ /\b([[:upper:]])\B/g);
    	printf "%s (%s)\n",  join("", @author_initials), $author;
    }

When that's run with and without UTF8 being true in the environment it
gives, on git.git:

    $ UTF8=0 perl author-initials.pl | sort | uniq -c |
    sort -nr | head -n 5
         99 JH (Junio C Hamano)
         35 JN (Jonathan Nieder)
         35 JK (Jeff King)
         20 JS (Johannes Schindelin)
         16 AB (Ævar Arnfjörð Bjarmason)
    $ UTF8=1 perl author-initials.pl | sort | uniq -c |
    sort -nr | head -n 5
         99 JH (Junio C Hamano)
         35 JN (Jonathan Nieder)
         35 JK (Jeff King)
         20 JS (Johannes Schindelin)
         16 ÆAB (Ævar Arnfjörð Bjarmason)

Acked-by: Jakub Narębski <jnareb@gmail.com>
Tested-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Tested-by: Simon Ruderich <simon@ruderich.org>

Signed-off-by: Junio C Hamano <gitster@pobox.com>

gitweb/gitweb.perl

@@ -6626,6 +6626,7 @@ sub git_blame_common {
 			$hash_base, '--', $file_name
 			or die_error(500, "Open git-blame --porcelain failed");
 	}
+	binmode $fd, ':utf8';
 
 	# incremental blame data returns early
 	if ($format eq 'data') {