Instruct man(1) to run the 'tbl' preprocessor

[havardAasen]

This is needed to get set the macro 'TW' with the table width. This was a new warning in groff 1.23.0

Can be tested with the command:

LC_ALL=C.UTF-8 MANROFFSEQ='' MANWIDTH=80 \
    man --warnings -E UTF-8 -l -Tutf8 -Z popt.3 > /dev/null

[pmatilai]

Hmm, this seems to turn one warning into another. Before:

troff::135: warning: cannot select font 'CW'
an.tmac::138: warning: tbl preprocessor failed, or it or soelim was not run; table(s) likely not rendered (TE macro called with TW register undefined)

After:

troff::137: warning: cannot select font 'CW'
troff::137: warning: cannot select font 'CW'
:480: warning: table wider than line length minus indentation

I suppose that's to be expected if the undefined TW stops processing that now continues.

But, I am boggling at the issue itself. popt.3 manual is 26 years old and all of a sudden it now needs a mystery magic '\" t sequence at the top? What? 😳

After some hunting I can see this: https://www.mail-archive.com/debian-devel@lists.debian.org/msg377307.html which points to https://manpages.debian.org/bookworm/man-db/man.1.en.html#DEFAULTS which explains that this is a means to run the tbl preprocessor as if it was specified on the groff command line, or something to that effect. It also does seem to be quite old, so adding it wont break compatibility.

So thanks for the patch. But this is a wake-up call to move popt man pages to markdown too, this is a little too arcane even for this old-school person.