gtk3: modify a method call with a deprecated argument style
gtk3: add a sample script a signal handler for main window to destroy properly
Merge pull request #248 from kitachro/buttonrb-quit

gtk3: make a sample program quit properly

Patch by kitachro. Thanks!!!
Merge pull request #247 from kitachro/buttonboxrb

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