Refactoring of statements returning Py_None

Refactored boilerplate statements
Py_INCREF(Py_None)/return(PyNone) into calls to
macro Py_RETURN_NONE, available since Python 2.4.
Merge remote-tracking branch 'archived/pull/52/head'

* archived/pull/52/head:
  Refactoring of statements returning Py_None