x86 update

[Stephen Weeks]

> I don't know if any big conclusions can be drawn, although I'm tempted to
> remark that for all of our complaining about the sparcity of registers on
> the x86, register pressure may not be that big an issue (at least for
> MLton generated code). 

The fact that you are seeing code after the very conservative register allocator 
runs on the CPS IL may have a lot to do with this.  Recall that it allocates a
variable permanently in a stack slot if that variable is ever live across a
nontail call.