Set tick labels for the x-axis.

        Also set the x-ticks positions to ensure the labels end up on
        the correct place.

        :param labels: list of labels for the ticks along the axis.

def set_xtick_labels(self, labels, style=None):
        """Set tick labels for the x-axis.

        Also set the x-ticks positions to ensure the labels end up on
        the correct place.

        :param labels: list of labels for the ticks along the axis.

        """
        self.ticks['xlabels'] = labels
        self.ticks['xlabel_style'] = style