This patch fixes some issues with the newly added
Tix.Grid widget:
- fixed entrycget() and entryconfigure()
- fixed typo in yview_moveto()
- replaced self with self._w in function calls
- changed xview() and yview() to accept parameters, as
in Tkinter
- added _dummyGrid class and fixed the ScrolledGrid
- added a few useful constants

-added methods:
    - anchor_clear()
    - anchor_set()
    - bdtype()
    - dragsite_set(), _get() and _clear() and
corresponding dropsite_() methods
    - edit_apply() and edit_set()
    - format_border() and format_grid()
    - geometryinfo()
    - index()
    - move_row() and move_column()
    - selection_set(), _get(). _clear(), _toggle() and
_includes()
    - size_row() and size_column()
    - sort_row() and sort_column()
    - unset()

I also added some (hopefully useful) docstrings.