Completed implementation of encrypt for salted password hashes

Now generating salted hashes if encrypt (Unix passwords) are in use. It's needs a second parameter if you want a salted password (The salt). As this don't need to be HEX I added an function that generating 16 bytes of letters, because this is more secure. If you don't like this just change it to gen_salt and remove the function.

Would be happy if this comes into the lemonldap ng because else i need to merge it into every version, because unix passwords are in use but don't want unsalted hashes. Thank you for reading