add support for head prefix attribute

[pgherveou]

Hi guys, since Facebook is using the prefix attribute on the head element to declare open graph namespace. Could we add it to the list of supported attributes?

this would be useful when generating templates with https://github.com/reactjs/express-react-views

see this link too for more details
http://stackoverflow.com/questions/8235687/open-graph-namespace-declaration-html-with-xmlns-or-head-prefix

[ledbruno]

This coulde be also usefull for SVG namespaced attributes. For instance, xmlns:xlink. Now, we are facing problems => Error: Namespace attributes are not supported. ReactJSX is not XML.

[eikeon]

FYI, it looks like data-prefix works re: Facebook picking up on the Open Graph namespace declaration.

[aweary]

The prefix attribute is now supported: https://jsfiddle.net/2377eovv/

See #4942