Implements a mechanism by which search engines can provide different
result orderings, and implements a 'by location' ordering within the
Solr search engine (available whenever the user starts their search
from within a course or activity).
Adds group support to the core search API and the Solr search engine.
This allows for:
* User searching by group (in the API only, no interface yet)
* Automatically restrict search results by group (in some cases like
separate-groups forums)
Adds a new 'Gradual reindex' link to the search areas page for each
area. When clicked, this takes you to a confirm prompt, and then
adds each context from that search area to the indexing queue.
The search areas page now displays the 'Additional indexing queue'
(if it is non-empty). The table shows the first 10 items in the
queue, and it also indicates the total number in case there are
more. (I don't think people really need to see the entire
contents of it, so I didn't implement paging.)
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).
