Feature to return an extra in the cursor that keeps the spinny going.

If a search provider returns an extra in the cursor with the key
SearchManager.CURSOR_EXTRA_KEY_IN_PROGRESS, and the value true, then
the spinny in the search dialog will not stop, but the cursor
contents will still be used to update the results. This way, partial
search results can be sent while the user is informed that the search
is still in progress.