Give compiler error if an origin state is defined multiple times in a transition table.

[K1ngmar]

The example below should not be allowed since it defines transitions from the idle state multiple times.

MSM::TransitionTable
<
    MSM::Row<Idle,
        MSM::Transition<LocalEvent::StartGame, StartingGame, None, None>,
        MSM::Transition<LocalEvent::StartGame, None, None, None>,
        MSM::Transition<LocalEvent::ShutDown, ShuttingDown, None, None>
    >,

    MSM::Row<Idle,
        MSM::Transition<LocalEvent::Something, Something, None, None>
    >
>;