String definitions were being used with a pointless leading double
quote. This syntax is used only to define strings containing leading
space characters. (You might also use it defensively if you're defining
one string whose contents start with the interpolation of another, and
the latter might interpolate leading space--but that is not the case
here.)
Remove unnecessary leading quotes from string definitions.
* doc/Guidebook.mn: Do it. Also annotate empty strings with comment.
* sys/unix/hints/include/gbdates-post.370: Don't put them back.
https://www.gnu.org/software/groff/manual/groff.html.node/Strings.html
Allow the hints file to apply a correct timestamp to
the Guidebooks prior to use.
Detect the NH_DATESUB in the Guidebook.mn or Guidebook.tex
files and replace the datestamping line that follows.
If git is available, it determines the hash of the last commit
applied to doc/Guidebook.mn, and then determines the date of
that commit. The interim Guidebook.dated.mn (or
Guidebook.dated.tex) gets the datestamp applied.
If git isn't available or doesn't correctly provide the hash
for doc/Guidebook.mn, it should just continue to use whatever
hard-coded date in the Guidebook.mn source file (it uses it
instead of the interim file).
