Replace private variable `$textdomain` with a plain text string.

See also:
http://markjaquith.wordpress.com/2011/10/06/translating-wordpress-plugins-and-themes-dont-get-clever/

git-svn-id: https://plugins.svn.wordpress.org/wp-seedbank/trunk@846586 b8457f37-d9ea-0310-8a92-e5e31aec5664
Better i18n, add missing labels for Batch Exchange form.

git-svn-id: https://plugins.svn.wordpress.org/wp-seedbank/trunk@846587 b8457f37-d9ea-0310-8a92-e5e31aec5664