remove salt from HashVerifier

Per conversation with @ircmaxell I conclude that encouraging the use of salts in this way is to be avoided. End-users following the practice of prepending/appending salts to passwords for hashing will have to write their own implementations, which should be relatively easy to do.
rename $encrypted to $hashvalue

Per conversation with @ircmaxell, I conclude the proper term is something related to 'hash' not to 'encrypt'