Version 3.7
After attempting an automatic update to my self-hosted WordPress install from version 3.6.1 to version 3.7, within the admin panel, the site returned a completely blank page… I was unable to log back in to the admin panel at all, and the public site was down as well. The resulting URL displayed in the window contained:
../wp-admin/upgrade.php?_wp_http_referer=%2Fwp-admin%2F
…and in the the error log (viewable via FTP) was the entry:
Call to undefined function wp_get_current_user() in /wp-includes/user.php on line 215
In the WordPress.org › Support » Installation forum, user photoMaldives had the fix posted here… nice job.