It turns out you can't adjust foreign_keys while a transaction is active,
so the upgraders that need to disable and re-enable them were not
working right and encountering foreign key violations.
Previously they were relative to the directory from which the client
was launched, meaning it usually started with ./_etiquette.
Now it should be more portable and less tight.
By default, photos with searchhidden do not appear in the search
results. This allows a small number of representative images from
a large album to appear in the results, while the rest can be
found on the album's page.
The same effect could be achieved with a tag and forbid search,
but tag searching has much higher cost and it would be more difficult
to implement as a default behavior without requiring lots of special
checks whenever listing tags etc.
