When rendering an audio or video shortcode in IE 6-8, call document.createElement() as a poor man's HTML5 shiv. see #24902.

Merges [24931] to the 3.6 branch.



git-svn-id: https://core.svn.wordpress.org/branches/3.6@24932 1a063a9b-81f0-0310-95a4-ce76da25c4cd