add an overdue class to Due dates in ticket lists

This treats Due the same as DueRelative in ticket lists.

share/html/Elements/RT__Ticket/ColumnMap

@@ -237,7 +237,15 @@ $COLUMN_MAP = {
     Due => {
         title     => 'Due', # loc
         attribute => 'Due',
-        value     => sub { return $_[0]->DueObj->AsString }
+        value     => sub {
+            my $date = $_[0]->DueObj;
+            # Highlight the date if it was due in the past, and it's still active
+            if ( $date && $date->IsSet && $date->Diff < 0 && $_[0]->QueueObj->IsActiveStatus($_[0]->Status)) {
+                return (\'<span class="overdue">' , $date->AsString , \'</span>');
+            } else {
+                return $date->AsString;
+            }
+        }
     },
     Resolved => {
         title     => 'Resolved', # loc