Delegated change events are called too early and too many times

[snurra]

Normal change events are triggered after all changes needed from a call to Backbone.Model.set has been made. However, delegated change events are triggered after each change made to the related attribute.

Example:

var Company = Backbone.RelationalModel.extend({
  relations: {
    employees: Backbone.Collection.extend({})
  }
});
var aCompany = new Company();
// Set 1
aCompany.set("name", "Kinship ltd");
// Set 2
aCompany.set("employees", [{ name: "Martin" }, { name: "Gustaf" }]);
// Set 3
aCompany.set({ name: "Kinship.com", employees: [{ name: "Henric"}, { name: "Mateusz" }]});

With current functionality:
Set 1 triggers 1 change:name event (after all attributes have been changed).
Set 2 triggers 2 change:employees events (one after each added employee).
Set 3 triggers 4 change:employees events (one after each removed and added employee) and 1 change:name event (after all attributes have been changed).

My suggestion is this:
Set 2 triggers 1 change:employees event (after all attributes have been changed).
Set 3 triggers 1 change:employees event and 1 change:name event (after all attributes have been changed).

Also, make sure that Set 2 triggers a change event after all related attributes have changed. (Not sure if this is currently done or not.)

This will bring delegated changes more in line with how normal changes behave (one change event for each changed attribute). Also, the model will be in a completely changed state instead of partial when the change event is triggered, just as with a normal change event.

Related to #7