added option for cron sync between ldap and moodle db see #MDL-29249

Hello,

thats my first pull request. I added an option for the cron job.
(see http://tracker.moodle.org/browse/MDL-29249)

I'm couldnt find informtions how to add default values in the database.
So that's not included. If you could provide some further informations about how to achieve this i'll be glad. ;)

alex