Twenty Thirteen: revert three changes to content attributes, props obenland. See #23550.

git-svn-id: http://core.svn.wordpress.org/trunk@23687 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Twenty Thirteen: adjust header max-width value for older IE browsers. Props jvisick77, see #23732.

git-svn-id: http://core.svn.wordpress.org/trunk@23688 1a063a9b-81f0-0310-95a4-ce76da25c4cd