Remove arbitrary string length limits

PyUnicode_FromFormat() and PyErr_Format() allocates a buffer of the needed
size, it is no more a fixed-buffer of 500 bytes.
diff --git a/Parser/tokenizer.c b/Parser/tokenizer.c
index 441d05a..556be46 100644
--- a/Parser/tokenizer.c
+++ b/Parser/tokenizer.c
@@ -590,7 +590,7 @@
         if (filename != NULL) {
             PyErr_Format(PyExc_SyntaxError,
                     "Non-UTF-8 code starting with '\\x%.2x' "
-                    "in file %.200U on line %i, "
+                    "in file %U on line %i, "
                     "but no encoding declared; "
                     "see http://python.org/dev/peps/pep-0263/ for details",
                     badchar, filename, tok->lineno + 1);