[m-rev.] for review: optimize field updates of packed args

[Zoltan Somogyi]

On Sun, 09 Sep 2018 08:33:09 +1000 (AEST), "Zoltan Somogyi" <zoltan.somogyi at runbox.com> wrote:

> For review by anyone.

The changes to du_type_layout.m and options.m were
NOT meant to be included in the diff.

Zoltan.