More fixes, more implementation!

YKmap.pm: fixed typo in SQL (key -> keys) in _suggest_usernames_sqlite()
YKmap.pm: Add detail to warning message in _suggest_usernames_sqlite(). Nice to know why there are no candidates.

radius-users: Import routines from rlm_yubico.pl for validating OTPs. This means YKmap.pm gets sucked in too, and we can use its routines.
radius-users: hashPassword used a buggered salt format. Fixed so hashes are salted.
radius-users: adduser accepts an OTP as a second argument, removing a second step of addyubikey when adding a user.
radius-users: adduser no longer resets an existing user's password. Use resetuser for that.
radius-users: adduser will not re-add an existing user (re-adding users makes no sense).
radius-users: Implmented addyubikey.
radius-users: addyubikey and adduser validate OTPs. Prevents associating a busted token with a user.
radius-users: Implemented delyubikey.