message: fix "unaligned" transmute
diff: @@ -396,9 +396,9 @@ impl<'a, 'tcx> EvalContext<'a, 'tcx> {
  "transmute" => {
  let src_ty = substs.type_at(0);
  let ptr = self.force_allocation(dest)?.to_ptr()?;
  - self.memory.begin_unaligned_read(false);
  + self.memory.begin_unaligned_write(/*aligned*/false);
  self.write_value_to_ptr(arg_vals[0], ptr.into(), src_ty)?;
  - self.memory.end_unaligned_read();
  + self.memory.end_unaligned_write();
  }
  "unchecked_shl" => {
  