Add option for locking translation sets when one article is being edited

In our setup of Drupal 6, we are using I18N and also the i18n sync module. It happens that when one person is editing a node and another person comes along to edit another node in the translation set, saving one of the nodes causes the other node to not be allowed to be saved.

Using the attached patch, when a person starts editing one node in the translation set, it causes the content locking messages to appear on any other nodes in the translation set. This helps prevent users from losing work.

Let me know if you have any questions or concerns with this.

Trevor