add parentheses to the output where required for disambiguation

Messages of the -Wbase level now print STYLE:. Since this
causes horrible churn anyway, profit of the opportunity to stop
excessive testing, such that this is hopefully the last instance
of such chu

Messages of the -Wbase level now print STYLE:. Since this
causes horrible churn anyway, profit of the opportunity to stop
excessive testing, such that this is hopefully the last instance
of such churn. Consistently use OpenBSD RCS tags, blank .Os,
blank fourth .TH argument, and Mdocdate like everywhere else.
Use -Ios=OpenBSD for platform-independent predictable output.

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catch up with the recent eqn(7) improvements

Don't dereference NULL pointers when formatting missing denominators,
subscripts, superscripts, or "from" or "to" arguments.
Found by jsg@ with afl.