The pager widget will now show a dropdown menu of overflow pages in the
middle. This allows easy access to the First and Last pages and an
ability to select from any of the middle pages to jump to quickly.
* Signup: if entering an existing email, don't admit that the email
exists. Instead, send a specialized email to its address.
* Search: no longer search for users by email address.
* Login: always hash the incoming password on user not found, to take
constant time compared to when the user did exist.
* Fix a pagination bug when a private (shy account) views a non-friend's
photo gallery.