Renamed tkerror to _tkerror, default_root to _default_root.
(_substitute, _subst_prefix): move back into class Misc; added
widget Event attribute.
Added functions that return widgets or widget lists:
winfo_children; focus_get; grab_current.
(Pack.slaves, Place.slaves): return Widget objects instead of
pathnames.
Renamed __del__() to destroy() (because of circular refs, __del__
won't ever be called).
Added some names with explicit _set: focus_set, focus_default_set,
grab_set.
Added focus_default_none.
(Misc._getints): use tk.splitlist() instead of tk.split(), return
None if string empty.