Core Upgrader success statistics: Pass the version of WordPress we're upgrading from, as well as the version being upgraded to. Props nacin. See #25772 for trunk

Built from https://develop.svn.wordpress.org/trunk@26016


git-svn-id: http://core.svn.wordpress.org/trunk@25947 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Core Upgrader: Include an unmodified $wp_version in Core_Upgrader::upgrade(). This protects against cases where the global $wp_version has been modified. See #25772

Built from https://develop.svn.wordpress.org/trunk@26017


git-svn-id: http://core.svn.wordpress.org/trunk@25948 1a063a9b-81f0-0310-95a4-ce76da25c4cd