bug#35338: Line numbers lost despite line-number-display-limit

["積丹尼 Dan Jacobson" <jidanni@jidanni.org>]

Users who do C-f v line-number-display-limit will never learn about
line-number-display-limit-width, and vice versa. 100%!

Therefore each docstring needs to mention the other.

Else the user won't know about the secret second hidden factor,
and will be sure it is a bug.

By the way, line-number-display-limit-width's docstring should say what
nil will do, and/or how to always/never get numbers.

P.S., "If the average length of the lines near point is bigger than
this, then the line number may be omitted from the mode line."

"near", "may" ??! Well all I know is if we do
$ { perl -wle 'print "中華民國萬歲" x 99 for 9..99;' ; seq 1111;} >  /tmp/9
we start out with fat lines, and then end up with thin lines,
and we get line numbers for the first few screens, and then it gives up.
If at the bottom we do (what-line) then it remembers again, until we go
back to the fat lines, where it forgets, even if we do (what-line).
Anyway I bet these days the rest of emacs' brain is actually rather
quite aware of what line we are actually on, and just this
line-number-display-limit-width is left over from some older era...
less -M and more's '=' have no problem.