Update password.php

The password_compact library (@ircmaxeel)  must be run on PHP 5.3.7 or newer due to some correction on Blowfish.
Versions of PHP before 5.3.7 only support "$2a$" as the salt prefix: PHP 5.3.7 introduced the new prefixes to fix a security weakness in the Blowfish implementation.
More information on http://www.php.net/security/crypt_blowfish.php

If some reasons we cannot update the version of PHP, we can change the prefix use for the salt (from `$2y$` to `$2a$`).

This commit should correct the no password in database.