Improvements for curved quotes on Linux consule

This should help Emacs work better out-of-the-box on Linux consoles,
which have only limited support for displaying Unicode characters.
Also, undo the recent change that caused text-quoting-style to
affect quote display on terminals, so that the two features are
independent.  See Alan Mackenzie in:
http://lists.gnu.org/archive/html/emacs-devel/2015-09/msg00244.html
Finally, add a style parameter to startup--setup-quote-display,
so that this function can also be invoked after startup, with
different styles depending on user preference at the time.
* configure.ac: Check for linux/kd.h header.
* doc/emacs/display.texi (Text Display): Document quote display.
* doc/lispref/display.texi (Active Display Table):
* etc/NEWS:
* lisp/startup.el (startup--setup-quote-display, command-line):
text-quoting-style no longer affects quote display.
* doc/lispref/frames.texi (Terminal Parameters): Fix typo.
* lisp/international/mule-util.el (char-displayable-p):
* lisp/startup.el (startup--setup-quote-display):
On a text terminal supporting glyph codes, use the reported
glyph codes instead of the terminal coding system, as this
is more accurate on the Linux console.
* lisp/startup.el (startup--setup-quote-display):
New optional arg STYLE.
* src/fontset.c (Finternal_char_font):
Report glyph codes for a text terminal, if they are available.
Currently this is supported only for the Linux console.
* src/termhooks.h (struct terminal): New member glyph-code-table.
* src/terminal.c [HAVE_LINUX_KD_H]: Include <errno.h>, <linux/kd.h>.
(calculate_glyph_code_table) [HAVE_LINUX_KD_H]: New function.
(terminal_glyph_code): New function.

3 files changed, 12 insertions, 5 deletions

diff --git a/doc/emacs/display.texi b/doc/emacs/display.texi
index 601a40bd176..92b0002990f 100644
--- a/doc/emacs/display.texi
+++ b/doc/emacs/display.texi
@@ -1480,6 +1480,15 @@ customizing the variable @code{glyphless-char-display-control}.
 @xref{Glyphless Chars,, Glyphless Character Display, elisp, The Emacs
 Lisp Reference Manual}, for details.
 
+@cindex curly quotes
+@cindex curved quotes
+@cindex escape-glyph face
+  If the curved quotes @samp{‘}, @samp{’}, @samp{“}, and @samp{”} are
+known to look just like @acronym{ASCII} characters, they are shown
+with the @code{escape-glyph} face.  Curved quotes that cannot be
+displayed are shown as their @acronym{ASCII} approximations @samp{`},
+@samp{'}, and @samp{"} with the @code{escape-glyph} face.
+
 @node Cursor Display
 @section Displaying the Cursor
 @cindex text cursor
diff --git a/doc/lispref/display.texi b/doc/lispref/display.texi
index 14e2cd363a4..b5ff9cb6e76 100644
--- a/doc/lispref/display.texi
+++ b/doc/lispref/display.texi
@@ -6533,10 +6533,8 @@ used when Emacs is displaying a buffer in a window with neither a
 window display table nor a buffer display table defined, or when Emacs
 is outputting text to the standard output or error streams.  Although its
 default is typically @code{nil}, in an interactive session if the
-locale cannot display curved quotes, or if the initial value of
-@code{text-quoting-style} specifies a preference for ASCII, its
-default maps curved quotes to ASCII approximations.  @xref{Keys in
-Documentation}.
+terminal cannot display curved quotes, its default maps curved quotes
+to ASCII approximations.  @xref{Keys in Documentation}.
 @end defvar
 
 The @file{disp-table} library defines several functions for changing
diff --git a/doc/lispref/frames.texi b/doc/lispref/frames.texi
index 16fc4958d1f..23590af7774 100644
--- a/doc/lispref/frames.texi
+++ b/doc/lispref/frames.texi
@@ -1781,7 +1781,7 @@ symbol) of @var{terminal}.  If @var{terminal} has no setting for
 @end defun
 
 @defun set-terminal-parameter terminal parameter value
-This function sets the parameter @var{parm} of @var{terminal} to the
+This function sets the parameter @var{parameter} of @var{terminal} to the
 specified @var{value}, and returns the previous value of that
 parameter.
 @end defun