misc testmachine improvements: It spends much more effort searching for bugs, and a new heuristic for helping to trigger them. Also fix a few formatting errors
unioning two suspended intmaps would always use the left hand one's combiner. Instead force the right hand one if their combiners differ
reified tests should also error on unreachable. Two of those unreachable cases are only possible (or at least easy) when reified
explicit values for intmap_tag for easier debugging
that was the wrong solution. drain itself should handle that case