parsers: use 'k' format for Py_BuildValue instead of 'n' because Python 2.4

'n' was introduced in Mercurial in 2b5940f64750 and broke Python 2.4 support in
mysterious ways that only showed failure in test-glog.t. Py_BuildValue failed
because of the unknown format and a TypeError was thrown ... but it never
showed up on the Python side and it happily continued processing with wrong
data.

Quoting https://docs.python.org/2/c-api/arg.html :

  n (integer) [Py_ssize_t]
    Convert a Python integer or long integer to a C Py_ssize_t.
    New in version 2.5.

  k (integer) [unsigned long]
    Convert a Python integer or long integer to a C unsigned long without
    overflow checking.

This will use unsigned long instead of Py_ssize_t. That is not a good solution,
but good is not an option when we have to support Python 2.4.

mercurial/parsers.c

@@ -873,12 +873,13 b' static PyObject *list_copy(PyObject *lis'
 	return newlist;
 }
 
-static int check_filter(PyObject *filter, Py_ssize_t arg) {
+/* arg should be Py_ssize_t but Python 2.4 do not support the n format */
+static int check_filter(PyObject *filter, unsigned long arg) {
 	if (filter) {
 		PyObject *arglist, *result;
 		int isfiltered;
 
-		arglist = Py_BuildValue("(n)", arg);
+		arglist = Py_BuildValue("(k)", arg);
 		if (!arglist) {
 			return -1;
 		}