Fix validate_inclusion_of + with_message

[mcmire]

This is a fix for #595.

---

It did not fail if the given message did not match the message on the
validation itself.

[mrageh]

@mcmire This can be fixed by adding in more conditions to handle boolean attributes, something like the below should fix it.

def disallows_value_outside_of_array?
   if attribute_type == :boolean
    case @array
    when [false, true], [true, false], [true], [false]
        Shoulda::Matchers.warn BOOLEAN_ALLOWS_BOOLEAN_MESSAGE
        return true
    when [nil]
       if attribute_column.null
         Shoulda::Matchers.warn BOOLEAN_ALLOWS_NIL_MESSAGE
         return true
       else
         raise NonNullableBooleanError.create(@attribute)
       end
     end
   end

  !allows_value_of(*values_outside_of_array, @low_message)
end

[mcmire]

@Adam89 This isn't the same issue as that. This is saying, if you use validate_inclusion_of with a custom message, and the validation doesn't have that message and is instead using the default message, your test should fail. Previously it just passed.