bug#20545: New minor mode Electric Punct

[Eli Zaretskii <eliz@gnu.org>]

> Date: Sat, 16 May 2015 14:20:39 -0700
> From: Paul Eggert <eggert@cs.ucla.edu>
> CC: 20545@debbugs.gnu.org
> 
> On further thought, the code affects global settings so it should be done only if FRAME is nil. Also, it should treat double-quotes like single-quotes, and the ASCII approximations should use straight quotes. This code is separable from Bug#20545, and is also separable from the issue of how to quote in doc strings, as the code is useful whenever text with English quotes appears on an obsolescent display lacking them. So I installed the attached patch. 

Yes, this global effect is not a Good Thing.  It means that a buffer
with these characters that is displayed on a TTY frame and on a GUI
frame will use the substitutes on both.

Btw, is set-locale-environment called when a new frame is created?  If
not, then this is not a proper place to install the display table, as
it won't DTRT when a new TTY frame is created in a running Emacs
session, and that frame displays on a terminal that doesn't support
these characters.

I think it would be better to install this as a window-specific
display table, using set-window-display-table, as part of setting up
the window showing the *Help* buffer.  WDYT?