further fix for collector #697 - multiple selections

lib/python/OFS/dtml/properties.dtml

@@ -129,7 +129,7 @@ property values, edit the values and click "Save Changes".
     </div>
     <dtml-elif "_.has_key(select_variable)">
     <div class="form-element">
-    <select name="<dtml-var id>:utf8:list" multiple
+    <select name="<dtml-var id>:utf8:list:string" multiple
       size="<dtml-var "_.min(7, _.len(_[select_variable]))">">
       <dtml-in "_[select_variable]">
          <option<dtml-if