* validates_multiparameter_assignments plugin

A Ruby on Rails plugin that adds "validates_multiparameter_assignments" method to ActiveRecord::Base.
Example:

class User < ActiveRecord::Base
  validates_multiparameter_assignments
end

This makes multiparameter assignment errors to be added to the model, rather than raising 
ActiveRecord::MultiparameterAssignmentErrors.
By default the error message is read from ActiveRecord::Base.default_error_messages[:invalid]. You can change the 
message by adding an option like this:

validates_multiparameter_assignments :message => " is not entered correctly."

This plugin is especially useful when you use date_select helper method in the view, where the user can enter invalid 
dates such as "Feb 31, 2006".

- Shinya Kasatani <kasatani at gmail.com>