gtk3: modify method calls with a deprecated argument style
gtk3/sample/misc/button.rb
gtk3: add a signal handler for main window to destroy properly
gtk3/sample/misc/checkbutton.rb
gtk3: remove a method call that raise an error on gtk3
gtk3/sample/misc/colorselection.rb
Merge pull request #249 from kitachro/buttonrb-gtk3

gtk3: make a sample script gtk3 ready

Patch by kitachro. Thanks!!!
Merge pull request #250 from kitachro/checkbuttonrb

gtk3: make a sample program quit properly

Patch by kitachro. Thanks!!!
Merge pull request #251 from kitachro/colorselectionrb-gtk3

gtk3: make a sample script gtk3 ready

Patch by kitachro. Thanks!!!