a CG type adaptive, canonicalizing & filtering serializer that is an
under-approximation mostly aimed at finding data races and deadlocks in programs
with a large number of scheduling points (= thread choices)
This came to bear by accidentally discovering that JPF often seems to finds
concurrency defects by just serializing the thread states, their topmost stack
frames and the objects directly referenced from there.
For non-scheduling points, we just fall back to serializing statics, all thread
stacks and all the data reachable from there