fix: delete()

The delete method does not delete product_stock record.
Typing error in delete product record debug log, sql iso sqlz
fix: _create()

add 'require_once DOL_DOCUMENT_ROOT.'/product/class/product.class.php';'
to htdocs/product/stock/class/mouvementstock.class.php _create method.
This to support product class instance used in function.
Merge pull request #1255 from fappels/develop

fix on product and mouvementstock classes