TinyMCE strips them by default, but if they're specifically added
to the allowed elements we should respect that setting.
Example PHP config:
$validEls = HtmlEditorConfig::get('cms')->getOption('extended_valid_elements');
$validEls .= ',script[src|type]';
HtmlEditorConfig::get('cms')->setOption('extended_valid_elements', $validEls);
Since that used to be the default shortcode notation
for our core "insert media" functionality, its important
to have this fixed and keep supporting "legacy" content
created with 3.0.
