Add a missing forward declaration for PyFileIO_Type. The _fileio module now compiles with --with-pydebug.

Modules/_fileio.c

@@ -44,6 +44,8 @@ typedef struct {
 	PyObject *weakreflist;
 } PyFileIOObject;
 
+PyTypeObject PyFileIO_Type;
+
 #define PyFileIO_Check(op) (PyObject_TypeCheck((op), &PyFileIO_Type))
 
 /* Note: if this function is changed so that it can return a true value,