Modification by Johannes Luthman of the built-in NetStim.mod of NEURON 6.1.
NB, this code has not been used with CVode.

Changes from NetStim:
    The output events can be set to follow gamma distributions of order 1-6,  
    where 1 corresponds to the original Poisson process generated by NetStim.mod.
    The gamma process is generated in the same way as that given by timetable.c
    in GENESIS 2.3.
    A refractory period has been added.
    The output length is determined by duration in ms instead of number of events.

Parameters:
    interval: 	mean time between spikes (ms)
    start:      start of first spike (ms)
    noise:      amount of randomness in the spike train [0-1], where 0 generates
                fully regular spiking with isi given by parameter interval.
    duration:   length in ms of the spike train.
    order:      Integers [1-6] giving the order of gamma distribution.
    refractoryPeriod (ms)
