Multiple categories in the product_category shortcode

Add the ability to input multiple categories separated by a comma in the
[product_category] shortcode.
IT languages update
Confirm buffer is not empty before erasing

Confirm file_exists before opening. For PHP 5.3 or earlier, check if
safe_mode is active to avoid errors.
Use wp_send_json() WordPress function for AJAX

The header(), json_encode(), and die(), functions are all executed with
a better logical routine that should provide consistent results.
Allow downloadable products URL to be relative
Introduce 'woocommerce_get_order_item_totals_excl_free_fees' filter

The new filter will allow plugins that add order item meta to choose to
display the free fee items on order details pages and emails.
Basic order factory class
get_order wrapper function for new factory
Replace new WC_Order calls with get_order
Created WC_Abstract_Order, extended by WC_Order
Restore get_order call in WC_Order constructor
WC_Order is default class for order factory
Added comment to indicate that WC_Order shouldn't be directly instantiated
Field show/hide options for stock fields and variations
Product admin/saving
Simplify get_children and use stock status rather than stock level
Conditional is no longer required
Add sanity check to stock status change
Only call the method to update stock when it changes
Hide status box for variables and handle save event