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.

cope with changes in BASE messages

churn related to the new style message about RCS ids

churn caused by the new Mdocdate messages, no easy way to avoid this :(

style message about missing blank before trailing delimiter;
inspired by mdoclint(1), and jmc@ considers it useful