Changed to present reference number in Print Invoices/Credit Notes if global $print_i...

Changed to present reference number in Print Invoices/Credit Notes if global $print_invoice_no = 0
Deleting of Locations was too easy. Implemented much more checks
Report Stock Check Sheet and 'Inventory Item Status' was wrong when Locations were selected
When producing advanced manufacture there should be errors when insuffient qoh in items (if 'Allow Negative Stock' is not marked)