Plots the histogram with Poisson (sqrt(n)) error bars
          - scale_errors_by multiplies the error bars by its argument
          - scale_histogram_by multiplies the histogram AND the error bars by its argument
          - plt thing to call .errorbar on (pylab, figure, axes, whatever the matplotlib guys come up with next)

def plot(self, normed=False, scale_errors_by=1.0, scale_histogram_by=1.0, plt=plt, errors=False, **kwargs):
        """Plots the histogram with Poisson (sqrt(n)) error bars
          - scale_errors_by multiplies the error bars by its argument
          - scale_histogram_by multiplies the histogram AND the error bars by its argument
          - plt thing to call .errorbar on (pylab, figure, axes, whatever the matplotlib guys come up with next)
        """
        if not CAN_PLOT:
            raise ValueError("matplotlib did not import, so can't plot your histogram...")
        if errors:
            kwargs.setdefault('linestyle', 'none')
            yerr = np.sqrt(self.histogram)
            if normed:
                y = self.normalized_histogram
                yerr /= self.n
            else:
                y = self.histogram.astype(np.float)
            yerr *= scale_errors_by * scale_histogram_by
            y *= scale_histogram_by
            plt.errorbar(self.bin_centers, y, yerr,
                         marker='.', **kwargs)
        else:
            kwargs.setdefault('linestyle', 'steps-mid')
            plt.plot(self.bin_centers, self.histogram, **kwargs)