a class is available for a callback entry.
* ext/tk/lib/tk.rb (after_cancel): add Tk.after_cancel(afterID) method.
* ext/tk/lib/tk.rb (array2tk_list): change from private module method
  of TkComm to public module method.
* ext/tk/lib/tk.rb (cget): add check that slot argument is not empty string.
* ext/tk/lib/tk.rb (configinfo): ditto.
* ext/tk/lib/tk/itemconfig.rb (itemcget): add check that slot argument
  is not empty string.
* ext/tk/lib/tk/itemconfig.rb (itemconfiginfo): ditto.
* ext/tk/lib/tk/entry.rb: add TkEntry#icursor and icursor= (alias of
  cursor and cursor= method).
* ext/tk/lib/tk/font.rb: improve font treatment when the font name is
  empty string.
* ext/tk/lib/tk/variable.rb: add :variable, :window and :procedure type.
* ext/tk/lib/tk/variable.rb: improve treatment of array-type tkvariable.
* ext/tk/lib/tkextlib/blt.rb: add commands for zooming.
* ext/tk/lib/tkextlib/blt/*: bug fix.
* ext/tk/lib/tkextlib/treectrl/tktreectrl.rb: bug fix and add methods
  to call TreeCtrl commands for bindings.
* ext/tk/sample/tkextlib/blt/*: new sample scritps.
* ext/tk/sample/tkextlib/treectrl/*: ditto.


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_1_8@8195 b2dd03c8-39d4-4d8f-98ff-823fe69b080e