Using unsupported options causes a load error due to missing variable

Adding an option to attr_encrypted that is not supported by Symmetric Encryption causes an exception due to the params variable not being passed to the warn.

I've set the variable to be passed and added a test to confirm. Having the unsupported option present is all that is really needed to test as it prevents load, but I've added an explicit test so it will be clear why it is there in future changes.

I discovered this when using the gem [tinfoil/devise-two-factor](github.com/tinfoil/devise-two-factor). This gem uses attr_encrypted's `:key` and `:mode` options [here](https://github.com/tinfoil/devise-two-factor/blob/master/lib/devise_two_factor/models/two_factor_authenticatable.rb#L12).