Rust updates

[David Piepgrass]

>>> The trouble with segmented stacks are:
>>>
>>> 1. they have a significant runtime penalty
>> Why?
> Extra instructions generated for each function.
Every function? Why?

>>> 2. interfacing to C code becomes problematic
>> Isn't it possible to auto-commit new pages when C code needs 
>> it?
...
> There's no way to predict how much stack arbitrary C code will 
> use.
Presumably one does not call arbitrary C code. Usually one knows 
what one might call in advance and can plan accordingly (and even 
if it is arbitrary, one at least knows *that* one is going to 
call C code and plan accordingly. Most C code doesn't allocate 
more than a few megabytes on the stack).