Cope with new na64utils-msadc API

This issue is devoted to some minor API changes introduced in new (after approximately v1.9) versions of the libna64util (to be finalized simultaneously with this issue).

Although the user API changes are subtle, internal design of the library has been deeply reworked. In the eponymous branch I will introduce a version update and ask for some testing. Please, report here on possible incompatibilities.

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