New event "order_status_changed_before_save"

[woutersamaey]

Description (*)

New event "sales_order_state_change" allows custom modules to detect an order state/status change and trigger appropriate actions. I've seen modules rewrite the order model because this was missing.

Very handy improvement.

Contribution checklist (*)

• Pull request has a meaningful description of its purpose
• All commits are accompanied by meaningful commit messages
• All automated tests passed successfully (all builds are green)

[kiatng]

I actually need this event in some of my projects. However, I fire it from _beforeSave:

    protected function _beforeSave()
    {
        // ...
        // Just before exiting the function.
        if ($this->getStatus() != $this->getOrigData('status')) {
            Mage::dispatchEvent('order_status_changed_before_save', ['order' => $this]);
        }
        return $this;
    }

It doesn't check for state changes as condition of firing, which is less granular; a state may not have changed while status changes. However, you can easily check state changes in the observer.

I like firing in _beforeSave because I know at this point the states of the order model have settled, ie, the states of its attributes, the order items, order history, etc., have settled and are ready to be saved. I can also change the order's attributes in the observer and know that it will be saved.

[woutersamaey]

Updated this PR to reflect @kiatng example. This is indeed better.

[luigifab]

Could you add the new event into EVENTS.md.
Personally I would have used !=, but never mind.

[fballiano]

I think this one could be merged as it is (since it's not modifiable by other admins) and then I'll modify EVENTS.md in another PR.

[fballiano]

oops, it's not mergeable because of conflicts and only @woutersamaey can fix them

[fballiano]

completed via #2927