This makes it possible to pass additional options through Validators to message
generation. E.g. plugin authors want to add validates_presence_of :foo, :format
=> "some format".
Also, cleanup the :default vs :message options confusion in ActiveModel
validation message generation.
Also, deprecate ActiveModel::Errors#add_on_blank(attributes, custom_message) in
favor of ActiveModel::Errors#add_on_blank(attributes, options).
Original patch by Sven Fuchs, some minor changes and has been changed to be applicable to master again
[#4057 state:committed]
Signed-off-by: Jeremy Kemper <jeremy@bitsweat.net>