Background Updates: Record Plugin & Theme update statistics like we for for Core updates, Pass Plugin/Theme update objects into the Background updater for consistency with Core & Translations. See #27633

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Background Updates: Fix two variable typos in r27905

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git-svn-id: http://core.svn.wordpress.org/trunk@27737 1a063a9b-81f0-0310-95a4-ce76da25c4cd