[m-rev.] for review: move towards packing args with secondary tags

[Zoltan Somogyi]

For review by anyone, but I would like Julien to have a look at
the diff to uint*.m, because I don't know the right casts for C# and Java.
This could happen post commit, since having an incomplete implementation
of a new predicate in some unannounced modules for a day or two
should not pose any problems.

Zoltan.
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