PolymorphicComboAccessor
========================

Allows an easy accessor for polymorphic associations.

Example:

class ServiceRecord < ActiveRecord::Base
  belongs_to :serviceable, :polymorphic => true
end

class Plane < ActiveRecord::Base
  has_many :services, :as => :serviceable
end

class Car < ActiveRecord::Base
  has_many :services, :as => :serviceable
end

plane = Plane.create
car = Car.create

service_record = ServiceRecord.new(:serviceable => plane)
service_record.serviceable_type_and_id #=> "plane_1"
service_record.serviceable_type_and_id = "car_1"
service_record.serviceable #=> car