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.

Complete overhaul of the mandoc(1) test suite.
* Test the recently introduced -Tman output mode, too.
* Specify date and OS arguments in all tests.
* Remove the kludge of sed(1)ing away the page footer lines.
* New make(1) variables SKIP_TMAN, SKIP_GROFF.
* Drop obsolete, clumsy make(1) variable GROFF_TARGETS.
* Delete obsolete mdoc/Bl/E*.sh error reporting tests.
* Silence char/N/basic.
* New targets:
- ascii, ascii-clean - to run -Tascii tests only
- tman, tman-clean - to run the new -Tman tests only
- obj-clean - maintainer only, needed before groff-clean and groff
- groff-clean - maintainer only, affects checked-in files

major update of the mandoc test suite:
* add various new and extend a few existing tests
* stop using Mdocdate to ease syncing with NetBSD