Enable syncing of certain data between WordPress users and CiviCRM contacts

CiviCRM does not synchronize changes between WordPress users and CiviCRM contacts after initial creation via synchUser.

If contact information changes in CiviCRM (notably email address) or WP if the sync is run again, duplicate contacts are created.

Christian Wach has created a WP plugin (dependent on 4.6 or an updated CRM_Utils_System_WordPress) that synchronizes first name, last name and email address between CiviCRM and WP. I would recommend reviewing his work at https://github.com/christianwach/civicrm-wp-profile-sync and incorporate into civicrm-wordpress. As his plugin uses WP specific hooks, we will need to make sure these can all work from CiviCRM (they shoud),