FIX "Insert Link" and other TinyMCE loading bugs (fixes #8327)

Caused by SS loading a URL with html entities (&amp;)
through the Requirements API, which only works when directly
inserted into the HTML template (standard behaviour),
but garbles the URL GET parameters when loaded via the jQuery.ondemand
JavaScript/XHR logic.

It didn't fail the request, just meant that tiny_mce_gzip.php wasn't
getting all the required options from the GET parameters.
And since this newly loaded file contains the same JS globals,
it would override previously loaded (correct) state.