Updates: When a failed Background Update occurs, only show the failed update nag if the user hasn't yet updated if it was an early abort.

Merges [26186] from 3.8 to the 3.7 branch.

props SergeyBiryukov.
fixes #25887.

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git-svn-id: http://core.svn.wordpress.org/branches/3.7@27715 1a063a9b-81f0-0310-95a4-ce76da25c4cd