Adds a message about disabling multiple values on custom field form (#12251).

git-svn-id: svn+ssh://rubyforge.org/var/svn/redmine/trunk@11168 e93f8b46-1217-0410-a6f0-8f06a7374b81

config/locales/da.yml

@@ -1093,3 +1093,5 @@ da:
   label_in_the_next_days: in the next
   label_in_the_past_days: in the past
   label_attribute_of_user: User's %{name}
+  text_turning_multiple_off: If you disable multiple values, duplicate values will be
+    removed in order to preserve only one value per item.