skeletons: make the eof token translatable if i18n is enabled

* src/output.c (has_translations): New.
(prepare_symbol_names): Translate endtoken if the user already
translated tokens.

* examples/c/bistromathic/parse.y, src/parse-gram.y: Simplify.

src/parse-gram.h

@@ -77,7 +77,7 @@ extern int gram_debug;
 # define GRAM_TOKENTYPE
   enum gram_tokentype
   {
-    GRAM_EOF = 0,                  /* "end of file"  */
+    GRAM_EOF = 0,                  /* $end  */
     GRAM_ERRCODE = 1,              /* error  */
     GRAM_UNDEF = 2,                /* $undefined  */
     STRING = 3,                    /* "string"  */