Bug 699597 - EBookSqlite: Use UNION for autocomplete queries

The sqlite query planner does a really bad job here. It ought to realise
that it could do the searches on fields in folder_id directly from the
folder_id table, indices and all.

So recogise this case for ourselves and rephrase it so the query planner
doesn't do so badly. If it's just a logical 'OR' of a bunch of conditions,
some of which are auxiliary fields and some are not, then use a basically
hand-crafted query using UNION to make sure sqlite notices the fast way
to do it.

This takes the autocomplete query on my 237000-entry EWS GAL from about
1700ms to 6ms.

Yes, it's an icky special case and it *really* ought to be considered
a sqlite bug. But it's an important special case because the user is
waiting for it while they type and delays are really noticeable. And
it's a *big* win.

Discussed at
https://www.mail-archive.com/sqlite-users@sqlite.org/msg86350.html
https://www.mail-archive.com/sqlite-users@sqlite.org/msg86643.html