Fix 'format not a string literal' error

Thanks to Francois Andriot
(cherry picked from commit 592d3b6311)

src/translators/btparse/bibtex_ast.c

@@ -57,7 +57,7 @@ static void dump (AST *root, int depth)
 void dump_ast (char *msg, AST *root)
 {
    if (msg != NULL)
-      printf (msg);
+      printf ("%s", msg);
    dump (root, 0);
    printf ("\n");
 }

src/translators/btparse/error.c

@@ -88,7 +88,7 @@ void print_error (bt_error *err)
 
    if (err->filename)
    {
-      fprintf (stderr, err->filename);
+      fprintf (stderr, "%s", err->filename);
       something_printed = TRUE;
    }
    if (err->line > 0)                   /* going to print a line number? */
@@ -111,7 +111,7 @@ void print_error (bt_error *err)
    {
       if (something_printed)
          fprintf (stderr, ", ");
-      fprintf (stderr, name);
+      fprintf (stderr, "%s", name);
       something_printed = TRUE;
    }