Fix minor glitches from ‘format’ reversion

* doc/lispref/strings.texi (Formatting Strings):
After reversion, ‘text-quoting-style’ is documented in ‘Keys in
Documentation’, not below.
* src/syntax.c (Finternal_describe_syntax_value):
Prefer AUTO_STRING to build_string where either will do, as
AUTO_STRING is a bit faster.

doc/lispref/strings.texi

@@ -948,7 +948,7 @@ the width specifier normally consists of spaces inserted on the left:
 If the width is too small, @code{format} does not truncate the
 object's printed representation.  Thus, you can use a width to specify
 a minimum spacing between columns with no risk of losing information.
-In the following three examples, @samp{%7s} specifies a minimum width
+In the following two examples, @samp{%7s} specifies a minimum width
 of 7.  In the first case, the string inserted in place of @samp{%7s}
 has only 3 letters, and needs 4 blank spaces as padding.  In the
 second case, the string @code{"specification"} is 13 letters wide but
@@ -995,8 +995,12 @@ specifier, if any, to be inserted on the right rather than the left.
 If both @samp{-} and @samp{0} are present, the @samp{0} flag is
 ignored.
 
+@cindex curved quotes
+@cindex curly quotes
   The flag @samp{q} quotes the printed representation as per the
-variable @samp{text-quoting-style} described below.
+variable @samp{text-quoting-style}.  @xref{Keys in Documentation}.
+Typically it uses curved single quotes @t{‘like this’} as in the
+following example.
 
 @example
 @group

src/syntax.c

@@ -1333,9 +1333,11 @@ DEFUN ("internal-describe-syntax-value", Finternal_describe_syntax_value,
     insert_string (" (nestable)");
 
   if (prefix)
-    insert1 (Fsubstitute_command_keys
-	     (build_string
-	      (",\n\t  is a prefix character for `backward-prefix-chars'")));
+    {
+      AUTO_STRING (prefixdoc,
+		   ",\n\t  is a prefix character for `backward-prefix-chars'");
+      insert1 (Fsubstitute_command_keys (prefixdoc));
+    }
 
   return syntax;
 }