* ext/tk/lib/tk.rb: better operation for SIGINT when processing callbacks.
* ext/tk/lib/tk/msgcat.rb: ditto.
* ext/tk/lib/tk/variable.rb: ditto.
* ext/tk/lib/tk/timer.rb: ditto.
* ext/tk/lib/tk/validation.rb: add Tk::ValidateConfigure.__def_validcmd()
  to define validatecommand methods easier
* ext/tk/lib/tk.rb (_genobj_for_tkwidget): support autoload Tk ext classes
* ext/tk/lib/tk/canvas.rb and so on: remove the parent widget type check
  for items (e.g. canvas items; depends on the class) to avoid some troubles
  on Tk extension widget class definition.
* ext/tk/lib/tkextlib/: add Iwidget and TkTable extension support
* ext/tk/sample/tkextlib/: add samples of Iwidget and TkTable


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_1_8@6630 b2dd03c8-39d4-4d8f-98ff-823fe69b080e