switcher.cpp doesn't get updated when switch is changed, just when an input is changed

[eloimaduell]

We should be able to make swithcer output the correct value when we're not changing the input values but the switcher value.

I need to use the switcher in a situation where the inputs don't change ... just the switcher value.

Maybe it's solvable with a Mapper node, but I guess this option should be implemented.