Pass correct 'type' parameter to 'upgrader_process_complete' action in Theme_Upgrader.

props bamadesigner.
fixes #25882 for trunk.
Built from https://develop.svn.wordpress.org/trunk@26049


git-svn-id: http://core.svn.wordpress.org/trunk@25974 1a063a9b-81f0-0310-95a4-ce76da25c4cd