before can test
	commands for speed manager
	write trivial initial settlement to get data array right
	write out layout data on crash
	check that everything in Train and Segment is init'd
	do lay_train in resolution, or moral equivalent
	set points under existing trains according to existing movposcomb

dunno but maybe before can test
	wiring to gui display

things not yet considered at all in safety code
	coming up against points the wrong way
	min. curve specifications
	crossovers

initialise safety_state with appropriate stuff



make safety stop not be estop
check safety stop polarity is enough to cope with that