Add a default value for "stage" (0) in Index.add

pygit2.c

@@ -1322,9 +1322,9 @@ static PyObject *
 Index_add(Index *self, PyObject *args) {
     int err;
     const char *path;
-    int stage;
+    int stage=0;
 
-    if (!PyArg_ParseTuple(args, "si", &path, &stage))
+    if (!PyArg_ParseTuple(args, "s|i", &path, &stage))
         return NULL;
 
     err = git_index_add(self->index, path, stage);

test/test_index.py

@@ -67,7 +67,7 @@ class IndexTest(utils.RepoTestCase):
 
         sha = '0907563af06c7464d62a70cdd135a6ba7d2b41d8'
         self.assertFalse('bye.txt' in index)
-        index.add('bye.txt', 0)
+        index.add('bye.txt')
         self.assertTrue('bye.txt' in index)
         self.assertEqual(len(index), 2)
         self.assertEqual(index['bye.txt'].sha, sha)