Update of Magento stock quantity: reduced the memory footprint and improved


performance by using read() instead of browse() and proceeding by steps of 1000
records at a time.

Original proposal on Launchpad: https://code.launchpad.net/~camptocamp/openerp-connector-magento/7.0-update-stock-1330450/+merge/223393

Fixes https://code.launchpad.net/bugs/1330450