bug#35434: [<8; 36; 7m26.2; terminal emacs: continuation line indicator missing when word wrapping is enabled

[Eli Zaretskii <eliz@gnu.org>]

> From: Luis Gerhorst <privat@luisgerhorst.de>
> Date: Fri, 26 Apr 2019 10:07:58 +0200
> 
> 1. Start Emacs using 'emacs -Q --no-window-system'.
> 
> 2. Reduce the window width until the lines in the scratch buffer wrap
> around. Notice that Emacs shows a '\' at the end of each wrapped line.
> 
> 3. Type M-x toggle-word-wrap. Emacs no longer shows a '\' to indicate
> continuation lines. There is no way to tell whether the line contains a
> newline, or whether it has been wrapped.
> 
> Notice that if you do the same in graphical Emacs (i.e. start with
> 'emacs -Q'), the fringes do show an indicator for continuation lines,
> even with word wrapping enabled.

The canonical way of using this feature is with "M-x visual-line-mode",
not with toggle-word-wrap.  visual-line-mode takes care of removing
the fringe indicators as well, so the appearance on GUI frames and TTY
frames is the same: without continuation indicators.

toggle-word-wrap does part of the job of visual-line-mode, and frankly
I don't understand why the former even exists.

Making continuation glyphs appear in TTY frames shouldn't be hard, but
I don't know how important is that.