A typo in Gbk-1pg-sfx.mn resulted in " /" as a "last word" on the
end-of-data marker line of the intermediate 12345 line single page.
That was effectively invisible because it immediately got deleted
during the post-processing which strips off that marker through to
the end (producing a 5266 line single page at present).
Update sys/unix/Makefile.doc to be able to build Guidebook.dat, an
unpaginated copy of the plain text Guidebook. It's generated from
the 'roff source rather than by attempting to post-process the
regular text Guidebook.
No doubt there are easier ways to do this.
PatR