Expose the current mode stack length.

This is kind of weird, as the function doc suggests. What I'm trying to do: I have a mode on top of the stack. Halfway through the animation this mode manages, I want to remove all of the modes under it (it's a screen wipe). Some time later, I insert a new mode underneath this one and then finish what I'm doing and pop to that new mode.

Initially I thought I could do a popAllModes(); push(mode), but during removal, my current mode (which I still need) gets disposed, so that doesn't work. If there is a better (or more flashbangy) way to accomplish this than to expose the stack length and then removeMode(0) N times, I'm all ears.