Make sure the pings are only sent once per URL for a given post. props dllh. fixes #23217.

git-svn-id: http://core.svn.wordpress.org/trunk@23571 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Twenty Twelve: enable live preview for Header Text Color in Theme Customizer. Change also removes an `!important` declaration (yay) in Custom Header CSS rules.

Props SriniG, fixes #23600.

git-svn-id: http://core.svn.wordpress.org/trunk@23572 1a063a9b-81f0-0310-95a4-ce76da25c4cd