Make text-quoting-style customizable. Introduce t and new meaning for nil.

A value of nil for text-quoting-style now means "no translation".  t means
"Use curved quotes if displayable".

* src/doc.c (text-quoting-style (function)): modify for new semantics.
(text-quoting-style (variable)): Amend the doc string, set the default value
to t.

* lisp/cus-start.el: (top level): Create a customize entry for
text-quoting-style in group display.

* etc/NEWS: Amend the entry for text-quoting-style.

* doc/emacs/display.texi (Text Display): Describe the translation of ASCII
quotes to curved quotes, and how to influence or inhibit it.

* doc/lispref/control.texi (Signalling Errors)
* doc/lispref/display.texi (Displaying Messages)
* doc/lispref/strings.texi (Formatting Strings): Describe binding
text-quoting-style to nil to inhibit unwanted quote translation.

* doc/lispref/help.texi (Keys in Documentation): Change text-quoting-style
from a variable to a user option.  Describe its changed set of values.  State
that it can be customized freely.

1 files changed, 3 insertions, 0 deletions

diff --git a/doc/lispref/control.texi b/doc/lispref/control.texi
index 401a999cf23..09435f57966 100644
--- a/doc/lispref/control.texi
+++ b/doc/lispref/control.texi
@@ -1108,6 +1108,9 @@ generates a message like @t{"Missing ‘foo’"} with matching curved
 quotes.  In contrast, a call using a format like @t{"Missing '%s'"}
 with only apostrophes typically generates a message like @t{"Missing
 ’foo’"} with only closing curved quotes, an unusual style in English.
+One way around this problem is to bind @code{text-quoting-style} to
+@code{nil} around the call to @code{error}; this causes the
+@acronym{ASCII} quote characters to be output unchanged.
 
 @strong{Warning:} If you want to use your own string as an error message
 verbatim, don't just write @code{(error @var{string})}.  If @var{string}