[Pharo-project] Bug fix for InputEventSensor (incomplete initialization)

Ready to be reviewed: http://code.google.com/p/pharo/issues/detail?id=5501 Cheers, Alexandre -- _,.;:~^~:;._,.;:~^~:;._,.;:~^~:;._,.;:~^~:;._,.;: Alexandre Bergel http://www.bergel.eu ^~:;._,.;:~^~:;._,.;:~^~:;._,.;:~^~:;._,.;:~^~:;.