Nest doesn't accept integer spike_times -> correction proposed

Running the example tsodyksmarkram.py with nest gives an error:
> cd examples
> python tsodyksmarkram.py nest
There is no error if the line:
spike_source = sim.Population(1, sim.SpikeSourceArray(spike_times=numpy.arange(10, 100, 10)))
is replaced by:
spike_source = sim.Population(1, sim.SpikeSourceArray(spike_times=numpy.arange(10., 100., 10.)))

that is if the numpy array passed to spike_times is float, and not int.
The other backends (neuron and brian) seem to accept the int (at least, they don't give any error). I propose a small change in nest/populations.py that transforms the int array into a float array