Author: Michael Aherne
MDL-64587 xmldb: XMLDB option to add mandatory persistent fields.
http://git.moodle.org/gw?p=moodle.git;a=commit;h=495b4b412dc77e2e2780010b964ff6628160d6d9
http://github.com/moodle/moodle/commit/495b4b412dc77e2e2780010b964ff6628160d6d9
+ 3.7 en [addpersistent,tool_xmldb]
+ 3.7 en [persistentfieldsconfirm,tool_xmldb]
+ 3.7 en [persistentfieldscomplete,tool_xmldb]
+ 3.7 en [persistentfieldsexist,tool_xmldb]