Fix error on ie9 when rednering recurrence widget inside an overlay.

This PR attempts to fix the following two problems:
- The widget cannot be rendered on ie9 inside an overlay: On ie9 jquery internal method `$.buildFragment` crashes when the `defer` attribute is set. This method is used by `plone.app.querytools` when loading into an overlay. (`defer` should only be used, when there is an external script, according to http://www.w3schools.com/tags/att_script_defer.asp)
- Subsequent-error, when removing `defer`: On ie9 js-code loaded into an overlay seems to be executed twice, the first time the current page's globals are not available.