Add about.php text/tabs to credits.php and freedoms.php. (Caution: Styles may...

Add about.php text/tabs to credits.php and freedoms.php. (Caution: Styles may settle during shipping.) see #18742.

git-svn-id: https://core.svn.wordpress.org/trunk@19136 1a063a9b-81f0-0310-95a4-ce76da25c4cd