strange real timings partly explained

[Matthew Fluet]

> Yikes:  Real64.real objects are not aligned mod 8.  This is bad.  It costs us
> CPU time, and also makes lots of test relatively unreproducible  since  where
> you end up mod 8 can make a big difference.

I'm guessing that this is true in both the heap and the stack.  I know
that in the stack real elements are aligned mod 8 relative to the stack
top, but there is nothing that ensures that stack frames have sizes that
are aligned mod 8.  This would be easy enough to change, I think.