Add the version string to wp-content.css to avoid tenacious caching woes. see #27320.

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Avoid an undefined function due to `/wp-admin/includes/dashboard.php` being included too late. props obenland. fixes #27457.

Built from https://develop.svn.wordpress.org/trunk@27630


git-svn-id: http://core.svn.wordpress.org/trunk@27473 1a063a9b-81f0-0310-95a4-ce76da25c4cd