[ticket/14733] Support increasing hashing cost factor
* marc1706/ticket/14733:
[ticket/14733] Make sure detect_algorithm() works correctly and add tests
[ticket/14733] Extend passwords driver_interface in rehashable_driver_interface
[ticket/14733] Use new interface to preserve backwards compatibility
[ticket/14733] Use default cost factor in bcrypt constructor
[ticket/14733] Support increasing hashing cost factor