Salt generated as base64, but interpreted as UTF-8

[davidosborn]

The Salt.generateAsBase64String function produces a string that is the base64 representation of a random byte sequence. The PBKDF2.generateKey function takes the salt as a string but interprets it as a UTF-8 string. Since the salt is actually a base64 string, and not a UTF-8 string, there is some loss in the available range.