I've made the changes to merge the OnDemand code back into the standard ThreadGroup.
This means it's now trivial for users to switch between the different startup types. I hope I've not broken anything ... There's probably still some tidying up that could be done. For example, StandardJMeterEngine still creates the JMeterThread instances at the start. It might be better to make the thread group class responsible for handling these, so the additional objects are not created until needed. BTW, my French is not up to translating the delayed_start property entry - please can someone else fix that so the tests no longer fail? Thanks!
