zern benchmark

[Stephen Weeks]

> It seems that replacing Unsafe.Real64Array with Real64Array was a late
> change; the Real64Array structure doesn't have a create function, so I was
> getting compilation errors.  The fix is to rewrite mkRealArray:
> 
>     val mkRawArray   = fn n => A.array(n, 0.0)
> 
> Also, the benchmark program didn't make any indication of compilation
> failure in the log.

Whoops.  Fixed.  Thanks.  The benchmark program now at the very end prints out a
list of benchmarks that failed under all compilers.