Verify tags used in the gallery shortcode.



git-svn-id: http://core.svn.wordpress.org/branches/3.4@23318 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Use correct escaping function. props duck_.



git-svn-id: http://core.svn.wordpress.org/branches/3.4@23323 1a063a9b-81f0-0310-95a4-ce76da25c4cd