`_action_done` could unlink a quant. This happens when moving a product from a
location to another one and makes null the quantity of this product in one of
theses locations. In this case, we unlink the quant because it is now useless
and could be confusing on reports based on quants.
The unwanted side effect is that unlinking a record will invalidate the cache. In
some pathologic cases, like making an inventory adjustment of 600 products
and reseting their quantity back to 0, the time of the operation is around 15
minutes. With this patch that tries to work carefully with the cache invalidation,
the same operations takes around 15 secondes.
This commit do not unlink quant anymore, instead it use a 'garbage
collector' on quants without quantity. The garbage collector is trigger
on the scheduler and when the user open the inventory view.
Arnold Moyaux
c0d7a05730