handle event change, for event thrower, leaks in label and list
	modified:   GuiTest/TestGui.cpp
	modified:   GuiTest/TestGui.h
	modified:   GuiTest/TestTabItem.cpp
	modified:   GuiTest/TestTabItem.h
	modified:   Sample/SampleState.cpp
	modified:   Sample/SampleState.h
	modified:   StiGame/EventListener.cpp
	modified:   StiGame/EventListener.h
	modified:   StiGame/EventThrower.cpp
	modified:   StiGame/GuiState.cpp
	modified:   StiGame/Label.cpp
	modified:   StiGame/List.cpp
	modified:   StiGame/Viewport.cpp
trying to investigate memory leaks
	modified:   StiGame/Button.cpp
	modified:   StiGame/GuiState.cpp
	modified:   StiGame/Label.cpp
	modified:   StiGame/Viewport.cpp