Twenty Thirteen: update RTL styles to match changes in r24524, props obenland. See #23850.

git-svn-id: http://core.svn.wordpress.org/trunk@24536 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Twenty Thirteen: cleanup for functions.php file, props obenland. See #24653.

git-svn-id: http://core.svn.wordpress.org/trunk@24537 1a063a9b-81f0-0310-95a4-ce76da25c4cd