Allow to change a packing and keep it sync with Magento

Trouble:

We want to be able to replace or add a product during the packing process. OpenERP has no problem with that, but Magento does !

Solution:

Re-use part of Camptocamp work that add a button in packing line to replace a product. Override the account invoice creation method to replace the replaced product (without modifying the price). Add the added product into the invoice with a null price.

When calling the Magento API's, give it a dict of replace/added product.

Add in Magento the possibility to handle the product replacement without canceling the order. This should be transparent for us, even if it'll work this way on Magento side.

We need to have the packing object created on magento side because at the end, we'll be able to debit the payment at delivery time, not order time. Most of the payment method allow this on packing confirmation (so we can't handle this through pdf like for invoice for example).

Note that we'll also need to impact the invoices there for warranty purpose. We think about simply replace the replaced product also in the invoice and add a comment on the line like "This product replace XYZ one". This way, we keep the revenue on the right product (the one really sent).