Set current user to 0 after each unit test.

This prevents $current_user, $userdata, and other user-related globals from
being polluted if a previous test does not properly reset the current user.

Props nacin, mnelson4.
Fixes #29712.

git-svn-id: https://develop.svn.wordpress.org/trunk@30001 602fd350-edb4-49c9-b593-d223f7449a82
Editor: use <button> instead of <a> for the Visual/Text buttons, make them focusable. Props afercia, fixes #27553

git-svn-id: https://develop.svn.wordpress.org/trunk@30002 602fd350-edb4-49c9-b593-d223f7449a82