minor fix for list template.

tw2/forms/templates/table_layout.mak

@@ -1,7 +1,7 @@
 <%namespace name="tw" module="tw2.core.mako_util"/>\
 <table ${tw.attrs(attrs=w.attrs)}>
    % for i,c in enumerate(w.children_non_hidden):
-    <tr class="${(i % 2 and 'even' or 'odd') + ((c.validator and c.validator.required) and ' required' or '') + (c.error_msg and ' error' or '')}" \
+    <tr class="${(i % 2 and 'even' or 'odd') + ((c.validator and getattr(c.validator, 'required', None)) and ' required' or '') + (c.error_msg and ' error' or '')}" \
      %if w.hover_help and c.help_text:
       title="${c.help_text}" \
      %endif