* ext/tk/lib/tk.rb: add __val2ruby_optkeys and __ruby2val_optkeys to
  help to convert option values between ruby and tcl.
* ext/tk/lib/tk/itemconfig.rb: add __item_val2ruby_optkeys and
  __item_ruby2val_optkeys to help to convert option values between
  ruby and tcl.
* ext/tk/lib/tk/radiobutton.rb: use __ruby2val_optkeys for 'variable'
  option (for the reason of backward compatibility).
* ext/tk/lib/tk/composite.rb: clarify the arguments of super().
* ext/tk/lib/tk/spinbox.rb: ditto.
* ext/tk/lib/tk/text.rb: ditto.
* ext/tk/lib/tk/validation.rb: ditto.
* ext/tk/lib/tkextlib/*: support to treat tkvariable-type
  configure options.


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_1_8@8957 b2dd03c8-39d4-4d8f-98ff-823fe69b080e