[m-rev.] for post commit review: scalar commons in the MLDS

[Zoltan Somogyi]

After this diff, the compiler generates the exact same output
in Java and C# grades as before.

For post-commit review by anyone. I would particularly like
comments on the differences (highlighted by XXXs) in how
mlds_to_cs.m and mlds_to_java.m treat scalar vs vector commons.
They look unnecessary to me; does anyone know an actual reason
for them?

Zoltan.
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