* ext/tk/lib/tk.rb: avoid trouble when finalize TclTkIp.
* ext/tk/lib/tk.rb, ext/tk/lib/tk/*: help to fix troubles when
use Ttk widgets on old Tk scripts.
* ext/tk/sample/*: update and add demo stcipts. some of them are
introduction about new features of Tcl/Tk8.5.
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_1_8@16544 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
