Renamed show-nonbreak-escape to nobreak-char-display.

etc/NEWS

@@ -691,9 +691,9 @@ appears between the position information and the major mode.
 *** New face `escape-glyph' highlights control characters and escape glyphs.
 
 +++
-*** Non-breaking space and hyphens are now prefixed with an escape
-character, unless the new user variable `show-nonbreak-escape' is set
-to nil.
+*** Non-breaking space and hyphens are now displayed with a special
+face, either nobreak-space or escape-glyph.  You can turn this off or
+specify a different mode by setting the variable `nobreak-char-display'.
 
 +++
 *** The parameters of automatic hscrolling can now be customized.