Wrong delivery note numbering when partial shipment

[Jose Maria Alzaga]

When stock_move_change_delivery_date is installed the numbering of delivery notes is acting differently as how standard does when a partial shipment is performed.
The shipped delivery note is the last one instead of the original. e.g. if the original one is OUT/001 for 10 units and you ship 4. The result is:
OUT/002 shipped 4 units
OUT/001 pendind 6 units backorder of OUT/002
It should be
OUT/001 shipped 4 units
OUT/002 pendind 6 units backorder of OUT/001

I enclosed the stock.py module with the fix as a proposal.