Up to version 1.22.4, groff_mdoc(7) only considered the first word
when comparing section headers. For example, ".Sh SEE ELSEWHERE"
and ".Sh SEE Em ALSO" were considered instances of a SEE ALSO
section. In groff-current, exact matches with no sub-macros are
required. Adjust mandoc behaviour.

While here, also fix a very minor mandoc bug, even though no
detrimental effect of the bug on formatting is known. While using
sub-macros in the .Sh HEAD is bad style, the parsers accept it, so
setting the section attribute on the HEAD needs to act recursively.

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.

first batch of -T markdown tests

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.

first batch of -T markdown tests