* getSelectionNames(): return an empty list instead of an empty tupple
  if empty. fix a bug that raises an error without selection_data.
* remove bogus docstrings.
* add some docstrings.
* fix typos.



git-svn-id: https://svn.erp5.org/repos/public/erp5/trunk@12678 20353a03-c40f-0410-a6d1-a30d3c3de9de