* ext/tk/*: Support new features of Tcl/Tk8.6b1 and minor bug fixes.
     ( [KNOWN BUG] Ruby/Tk on Ruby 1.9 will not work on Cygwin. )
* ext/tk/*: Unify sources between Ruby 1.8 & 1.9.
            Improve default_widget_set handling.
* ext/tk/*: Multi-TkInterpreter (multi-tk.rb) works on Ruby 1.8 & 1.9.
     ( [KNOWN BUG] On Ruby 1.8, join to a long term Thread on Tk
       callbacks may freeze. On Ruby 1.9, cannot create a second 
       master interpreter (creating slaves are OK); supported master
       interpreter is the default master interpreter only. )
* ext/tk/lib/tkextlib/*: Update supported versions of Tk extensions.
         Tcllib 1.8/Tklib 0.4.1  ==>  Tcllib 1.11.1/Tklib 0.5
         BWidgets 1.7            ==>  BWidgets 1.8
         TkTable 2.9             ==>  TkTable 2.10
         TkTreeCtrl 2005-12-02   ==>  TkTreeCtrl 2.2.9
         Tile 0.8.0/8.5.1        ==>  Tile 0.8.3/8.6b1
         IncrTcl 2005-02-14      ==>  IncrTcl 2008-12-15
         TclX 2005-02-07         ==>  TclX 2008-12-15
         Trofs 0.4.3             ==>  Trofs 0.4.4


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@24063 b2dd03c8-39d4-4d8f-98ff-823fe69b080e