committing 2.1.15 into branch

git-svn-id: https://plugins.svn.wordpress.org/eshop-shipping-extension/branches/2.1@781572 b8457f37-d9ea-0310-8a92-e5e31aec5664
applying 2.1.15 into trunk

git-svn-id: https://plugins.svn.wordpress.org/eshop-shipping-extension/trunk@781576 b8457f37-d9ea-0310-8a92-e5e31aec5664