fails:String#crypt returns a cryptographic hash of self by applying the UNIX crypt algorithm with the specified salt
fails:String#crypt returns '.' prepended to the string for each NULL byte the salt contains
fails:String#crypt raises an ArgumentError when the salt is shorter than two characters
fails:String#crypt calls #to_str to converts the salt arg to a String
fails:String#crypt raises a type error when the salt arg can't be converted to a string
fails:String#crypt taints the result if either salt or self is tainted
fails:String#crypt doesn't return subclass instances
