Fix jQuery exception when it's not defined

Fix jQuery check

Trying to evaluate jQuery when it is undefined would throw a ReferenceError to the console. Trying to retrieve it on the global window instead will result in it being undefined if not defined.

Fix to make jQuery-less async actually render the response

Prior to this commit, an async request would go out but the response would be ignored, regardless of result.

Don't html-escape the path when outputting JS

Allow render_async_cache to take a placeholder

You can now pass in the placeholder to render_async_cache like you can to render_async