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.
Make checkout form multipart
Allow downloadable products URL to be relative
Placeholder functions
Add filter to allow override the cache widget id
Removed ununsed global variables in local scopes
Remove ordering query args

If these are not removed right after use they will affect the remaining
queries on the page.
Merge pull request #5638 from coenjacobs/code-cleanup

Removed unused global variables in local scopes
Merge pull request #5628 from tszming/fix-cached-widget

Add filter to allow override the cache widget id
This should be static
Fix address format in plain text email
Add  2.1.11 read me
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
Support storing transaction id in payment_complete method
Store PayPal transaction id through payment_complete method