Converts integer fontsizes to a string specifying
        fontsize in pt.

def _fontsize(self, key, label='fontsize', common=True):
        """
        Converts integer fontsizes to a string specifying
        fontsize in pt.
        """
        size = super(BokehPlot, self)._fontsize(key, label, common)
        return {k: v if isinstance(v, basestring) else '%spt' % v
                for k, v in size.items()}