Bug fix to allow multiple realtime raster plots.
The previous usage of pylab.gca() during the refresh operation caused
only the foreground figure to be updated.

One may validate the proper behavior now with this example script:

#################################################

from brian import *
import pylab

if __name__ == '__main__':

    pylab.ion()

    eqs = '''
    dv/dt = (ge+gi-(v+49*mV))/(20*ms) : volt
    dge/dt = -ge/(5*ms) : volt
    dgi/dt = -gi/(10*ms) : volt
    '''
    P = NeuronGroup(300, eqs, threshold=-50*mV, reset=-60*mV)
    P.v = -60*mV
    Pe = P.subgroup(200)
    Pi = P.subgroup(100)
    Ce = Connection(Pe, P, 'ge', weight=1.62*mV, sparseness=0.02)
    Ci = Connection(Pi, P, 'gi', weight=-9*mV, sparseness=0.02)
    M1 = SpikeMonitor(Pe)
    M2 = SpikeMonitor(Pi)
    raster_plot(M1, newfigure=True, refresh=500*ms, showlast=1000*ms,
redraw=True)
    raster_plot(M2, newfigure=True, refresh=100*ms, showlast=1000*ms,
redraw=True)
    run(10*second)
    pylab.ioff()