display_name not regenerated on prefix/suffix changes

Since 1.2, we allow the users to define their own Idividual Contacts? prefixes an suffixes. This means the display name of a contact should change when its prefix and/or suffix changes (i.e., if we decide we want to use Junior instead of Jr, or, more importantly, when we want to localise the prefixes and suffixes).

After the user edits a prefix or a suffix, we should regenerate the display_name values in the civicrm_contact table for every contact that had the edited prefix/suffix selected.