Fix missing bar numbers when options get set inside 'all series'

To reproduce, replace the first plot function in example.html with:

```
$.plot("#placeholder", [dataVertical], {
    series: {
        bars: {
            show: true,
            barWidth: 0.9,
            numbers: {
                show: true,
                formatter: barnumberFormatter,
                font: '14pt Arial',
                fontColor: '#FF0000',
                // remove the next 3 lines to vertically center the values
                threshold: 0.25, // any value < 25% of the maximum data point will display above the bar
                yAlign: function(y) { return y; }, // shows numbers at the top of the bar
                yOffset: 5 // pixel offset so numbers are not right up on the edge of the top of the bar
            }
        }
    }
});
```