Tracing idea

[Edward Z. Yang]

I was thinking it might be useful if we had a per-thread circular buffer in
memory for which we pushed a pointer to the info table we had just entered.  In
the event of a crash, you could dump the contents of the buffer to see what
code had been recently executed.  To reduce overhead, one might only need to
record this information when we do a tail call, and not when the path can be
reconstructed from the stack.  (Obviously, you'd need to compile in debug mode,
and you'd probably want to also add an RTS flag).

What do people think?

Cheers,
Edward