This new API returns a list of contexts for each search area. This
allows the areas to be reindexed in a sensible order (roughly
speaking, newest first) and also allows this to be controlled by
each area.
An implementation in the forum module means that forums are ordered
by the date of the most recent discussion, so that active forums
will be reindexed early even if they were created a long time ago.
The search area API now includes a new function get_document_recordset
which should be implemented in preference to the older
get_recordset_by_timestamp. (It's also possible to implement both in
plugin search areas which need to work against older Moodle versions.)
Existing search areas without the new function will continue to work as
before (obviously without the new functionality).
