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.
Make checkout form multipart
Allow downloadable products URL to be relative
Placeholder functions
Remove ordering query args

If these are not removed right after use they will affect the remaining
queries on the page.
status report overrides table format

New tr for every extension being checked for overrides.
Update class-wc-query.php

Use 'term_id' instead of 'id' for the tax_query as described in WP codex: http://codex.wordpress.org/Class_Reference/WP_Query#Taxonomy_Parameters
Setters + wc_create_order + wc_update_order for #4169
Set correct post type
woocommerce_order_add_fee
fixed two syntax error in paypal gateway class
improved the order items names when is attributes, closes #5551
fixed some coding standards in includes/admin/meta-boxes/views/html-order-item.php
improved the test for get the term name
added some brackets
improved the tax name in order item fee
fixed some coding standards in includes/admin/meta-boxes/views/html-order-fee.php
fixed hard coded Edit string
display the transaction id in the order data meta box