{stonehorn dignitary} stacks.
{temporal mastery} stacks.
Does {mindslaver} stack?
I believe so
I'm going to say no and here's why:
In the other two cases you are adding or taking away things. With 'slaver, you are only changing control.
Let's say you use your Mindslaver to control player A, then in response player B uses THEIR Mindslaver on A, theirs would overwrite yours instead of taking over A's second turn.