Allows multiple valid tickets per (users, purpose) pair

In loginticket_create the comments read

There can only be one ticket at a time for any user, so if there already
exists a ticket for the given user then the existing ticket is replaced
by the newly generated one.

but there was no logic in the routine to handle this.

Taking note of loginticket_check_expiration, we've updated it with this logic. Patches are attached here for both Drupal 5 and Drupal 6 (per the version posted for issue #264816: Drupal 6 port).