Add a missing "rf.depth = 0;" to marshal_load().

Reported by Joe Smith.  This makes the CYGWIN tests pass;
it's a miracle it didn't fail on other platforms.
Seems like it was accidentally dropped (maybe a merge artifact?).

Python/marshal.c

@@ -1181,6 +1181,7 @@ marshal_load(PyObject *self, PyObject *f)
 		return NULL;
 	}
 	rf.strings = PyList_New(0);
+	rf.depth = 0;
 	result = read_object(&rf);
 	Py_DECREF(rf.strings);
 	Py_DECREF(data);