Author: Mark Johnson
MDL-68093 availability: Add support for private rule sets
This allows an availability plugin to indicate that a selected condition
should be considered "private", and therefore should never be shown to
users who don't satisfy the criteria. The availability_groups plugin
uses this to protect visibility of groups that are not visible to
non-members.
http://git.moodle.org/gw?p=moodle.git;a=commit;h=cab6e97c1fbf0a9d493092ed25f5d08fcf2f34e3
http://github.com/moodle/moodle/commit/cab6e97c1fbf0a9d493092ed25f5d08fcf2f34e3
+ 4.2 en [disabled_verb,core_availability]