Crypt improvements

[clobee]

Main change concerns the use of "SECURE_AUTH_SALT"

[jojobote]

Why do we want to check env variables for the just the salt and not vector too ? Good otherwise !

[clobee]

@jojobote I am now getting the Init Vector from the wp-config as well just like the the passphrase.
This makes it like a 2 factor authentication: Any attacker will need the wp-config.php and the database to a successful attack.