bug#26396: 25.1; char-displayable-p on a latin1 tty

[Kevin Ryde]

On a latin1 tty, char-displayable-p claims that almost all chars are
displayable, eg (char-displayable-p #x2022) => t.

I hoped when (terminal-coding-system) is iso-latin-1-unix that
char-displayable-p would say only relevant latin1 chars are displayable.

I believe this is how it was in emacs24 was (and which helped avoid a
lot of very unattractive \ display escaping, at least from code knowing
not to try to display the undisplayable).


In GNU Emacs 25.1.1 (i686-pc-linux-gnu, X toolkit, Xaw3d scroll bars)
 of 2017-01-01, modified by Debian built on x86-csail-01

Important settings:
  value of $LANG: en_AU.iso88591
  locale-coding-system: iso-latin-1-unix