[m-rev.] for post-commit review: four improvements to c_util.m

[Zoltan Somogyi]

I am posting each diff individually to make them easier to review.
For review by anyone. The changes get to the "stages 2 and 3 compare ok"
stage of a bootcheck in the C# and Java grades, though I didn't have the
patience to wait out the full bootchecks in those grades.

Zoltan.
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