parsers: fix typing issue when constructing Python integer object

The passed variable is a Py_ssize_t, not a long, and consequently should use
PyInt_FromSsize_t rather than PyInt-FromLong. Fixed based on warning from
Microsoft Visual C++ 2008.

mercurial/parsers.c

@@ -881,7 +881,7 b' static PyObject *index_headrevs(indexObj'
 
 		if (nothead[i])
 			continue;
-		head = PyInt_FromLong(i);
+		head = PyInt_FromSsize_t(i);
 		if (head == NULL || PyList_Append(heads, head) == -1) {
 			Py_XDECREF(head);
 			goto bail;