Display RT-Attach headers in history by linking the filename

It is possible recipients of the transaction saw the attachment via
email but can't see it via the web.  This should be improved in the
future, but it's an acceptable edge case at the moment since we avoid
storing the attachment twice.

share/html/Ticket/Elements/ShowMessageHeaders

@@ -78,6 +78,17 @@ unless ( $display_headers{'_all'} ) {
 my $ticket = $Message->TransactionObj->TicketObj;
 foreach my $f (@headers) {
     $m->comp('/Elements/MakeClicky', content => \$f->{'Value'}, ticket => $ticket, %ARGS);
+    if ($f->{'Tag'} eq 'RT-Attach') {
+        # Blat in the filename and linkify
+        my $att = RT::Attachment->new( $session{'CurrentUser'} );
+        $att->Load($f->{'Value'});
+        next unless $att->Id and $att->TransactionObj->CurrentUserCanSee;
+
+        $f->{'Value'} = sprintf '<a href="%s/Ticket/Attachment/%d/%d/%s">%s</a>',
+                                RT->Config->Get('WebPath'), $att->TransactionObj->Id, $att->Id,
+                                $m->interp->apply_escapes($att->Filename, qw(u h)),
+                                $m->interp->apply_escapes($att->Filename, 'h');
+    }
 }
 
 if ( $Localize ) {

share/html/Ticket/Elements/ShowTransactionAttachments

@@ -118,7 +118,7 @@ if ( $Transaction->Type =~ /EmailRecord$/ ) {
 
 # If the transaction has anything attached to it at all
 elsif (!$ShowHeaders)  {
-    @DisplayHeaders = qw(To From RT-Send-Cc Cc Bcc Date Subject);
+    @DisplayHeaders = qw(To From RT-Send-Cc Cc Bcc RT-Attach Date Subject);
     push @DisplayHeaders, 'RT-Send-Bcc' if RT->Config->Get('ShowBccHeader');
 }