The availability condition get_description method is called while
gathering data for the modinfo object. As such it is not safe to
call other functions which might rely on modinfo, such as format_string
(if using filters which access modinfo).
This change provides a mechanism to call format_string later, and also
a general callback to do other stuff later as well if needed. It uses
the same approach already taken to make activity names work correctly
in the availability_condition class.
This commit defines the new /availability root folder, with
/availability/classes, /availability/tests, and
/availability/condition where the condition plugins will live.
Condition plugin prefix is availability_, e.g. availability_date.
Rationale for this organisation:
1. I was originally going to put this in /lib/availability but
it has been pointed out that putting even more junk in lib
is probably bad.
2. 'availability' and 'condition' are the two names used in code
to refer to this system ($CFG->enableavailability).
3. The prefix has to be short enough to allow database tables
(although in practice I assume that condition plugins will not
normally contain database tables).
The new API includes a Boolean tree structure that controls the
availability of an item.
AMOS BEGIN
CPY [availabilityconditions,core_condition],[restrictaccess,core_availability]
CPY [enableavailability,core_condition],[enableavailability,core_availability]
CPY [configenableavailability,core_condition],[enableavailability_desc,core_availability]
AMOS END
