The search areas screen contains several options which are potentially
risky for a live site but can be triggered by accidentally clicking a
single button or link.
This change adds a confirmation prompt for all these options.
The enable/disable search area icon does not have a confirmation
prompt because this is nondestructive (you can just click the icon
again to change it back).
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.)
