If merging 2 contacts, one with reference, and another without, and being the target
one the contact without reference, the constraint is raised as the reference value
is copied before unlinking the other contact.
We avoid it disabling the constraint when merging.
Display the recompute button only after saving the settings if the order hase changed. Once the recompute is done, the buttons desapears.
Bedore this change it was not possible to recompute the partner names order since the button was only displayed after changing the order value but before saving the changes. When clicked, an error message was displayed since the action will force the reload of the page before saving the values...