c1-bugs:
    .serious one, should be easy to fix:
	when cleaning up after interruption (_{flat,sweep,text}_program)
	processing (cleaning up that is) is aborted when some clean up method
	fails
e4-bugs:
    .it does look as if the expression optimizer (if given the chance) destroys
	data of application defined types without calling the proper (per
	application defined type) clean up method (though only if
	__OPTIMIZE_USER_FUNCTIONS__, which is wisely not set)
