Fix the qty computation.
Fix the qty computation.

- Old code used `len(component.refs)` discarding any `manf#_qty`
  information.
- The code to consolidate `manf#_qty` values wasn't working.
Fixes #455

hildogjr/KiCost,hildogjr/KiCost,xesscorp/KiCost,xesscorp/KiCost,hildogjr/KiCost,xesscorp/KiCost