Fix switcher behaviour for multiple pure values.

[jterbraak]

When switcher receives a Poll with multiple pure values all will be rendered at the same time and none will get their remove event triggered.

I've added a useMemoized hook that should fix the issues introduced by useRant and useReflect but I'm not sure if this implementation is save to export.

[mikesol]

Apologies for the delay, I've been swamped with work but I'll look at this next week. Thanks for your patience.