Doesn't work with simultaneous events

[raimohanska]

Failing case:

    a = Bacon.Model()
    f = a.lens("first").log("first")
    l = a.lens("last").log("last")
    stuff = Bacon.Model.combine({f, l}).log("stuff")
    values = collect(stuff)
    a.set({first:"f", last:"l"})
    expect(values).to.deep.equal([{}, {first: "f", last: "l"}])

I stumbled upon this when testing Bacon.js 0.7.0 in a project.

[raimohanska]

Fixed in 0.3.13.

Problem was the "pingpong-prevention" logic that was based on modCount. Now it's based on a "modStack". Should be reliable. Has some performance penalty, though.