This contains a number of changes, but they all look clean and
straightforward based on reading the code. I tried killing the WeakArray
finalization process, then saving and restarting the image, and
everything came back fine. It's late in the release cycle, but this
change set may prevent serious and hard-to-debug problems for Squeak
users. It is relatively low risk, so I recommend including in 3.7 if
possible.

Very minor nit (that should not prevent inclusion in 3.7): InputSensor
class>>startUp should not be in this change set. It just adds an
unneeded carriage return to the source but otherwise does not change
anything.