Use angle brackets to mark i/o from descriptors

In this case use “<standard output>” and “<standard input>”, to make
it clear that it's not a file with such name, in the same way we do in
the reset of the code base.

scripts/Dpkg/Control/Info.pm

@@ -52,7 +52,7 @@ sub new {
     bless $self, $class;
     if ($arg) {
         if ($arg eq "-") {
-            $self->parse_fh(\*STDIN, _g("standard input"));
+            $self->parse_fh(\*STDIN, _g("<standard input>"));
         } else {
             $self->parse($arg);
         }

scripts/changelog/debian.pl

@@ -132,7 +132,7 @@ my $range = {
 my $changes = Dpkg::Changelog::Debian->new(reportfile => $label, range => $range);
 
 if ($file eq '-') {
-    $changes->parse(\*STDIN, _g("standard input"))
+    $changes->parse(\*STDIN, _g("<standard input>"))
 	or error(_g('fatal error occured while parsing input'));
 } else {
     $changes->load($file)

scripts/dpkg-gensymbols.pl

@@ -208,7 +208,7 @@ $symfile->clear_except(keys %{$od->{objects}});
 
 # Write out symbols files
 if ($stdout) {
-    $output = "standard output";
+    $output = _g("<standard output>");
     $symfile->save("-", package => $oppackage,
                    template_mode => $template_mode, with_deprecated => 0);
 } else {