I don't know what common stack sizes are any more.  Even on the same
platform, the main thread may have a different stack size than other
threads.  

Would it make sense to make this limit more platform-dependent?

I guess really good would be a way to handle C stack overflows more
gracefully, but that's for another era.

All said, let's try a 3x increase, *and* have a unittest that pushes the
limits to the max (both a case that is one short of the limit and a case
that is over the limit, and is expected to raise an exception).