yacc.c: add support for parse.error detailed

"detailed" error messages are almost like "verbose", except that we
don't double escape them, they don't get inner quotes, we don't use
yytnamerr, and we hide the table.

"custom" is exposed with the "detailed" tokens, not the "verbose"
ones: they are not double-quoted.

Because there's a risk that some people use yytname even without
"verbose", let's keep yytname (instead of yys_name) in "simple"
parse.error.

* src/output.c (prepare_symbol_names): Be ready to output symbol names
unquoted.
(prepare_symbol_names): Output both the old tname table, and the new
symbol_names one.
* data/skeletons/bison.m4: Accept 'detailed'.
* data/skeletons/yacc.c: When parse.error is 'detailed', don't emit
yytname and yytnamerr, just yysymbol_name with the table inside.
* tests/calc.at: Adjust.

src/output.c

@@ -139,13 +139,17 @@ static void
 prepare_symbol_names (char const *muscle_name)
 {
   /* We assume that the table will be output starting at column 2. */
+  const bool quote = STREQ (muscle_name, "tname");
   int j = 2;
   struct quoting_options *qo = clone_quoting_options (0);
   set_quoting_style (qo, c_quoting_style);
   set_quoting_flags (qo, QA_SPLIT_TRIGRAPHS);
   for (int i = 0; i < nsyms; i++)
     {
-      char *cp = quotearg_alloc (symbols[i]->tag, -1, qo);
+      char *cp =
+        symbols[i]->tag[0] == '"' && !quote
+        ? xstrdup (symbols[i]->tag)
+        : quotearg_alloc (symbols[i]->tag, -1, qo);
       /* Width of the next token, including the two quotes, the
          comma and the space.  */
       int width = strlen (cp) + 2;
@@ -192,6 +196,7 @@ prepare_symbols (void)
 
   /* tname -- token names.  */
   prepare_symbol_names ("tname");
+  prepare_symbol_names ("symbol_names");
 
   /* Output YYTOKNUM. */
   {