Fixes to the rendering of Flags below their data series

Previously if the label was below its data point, the connecting line was drawn over the label's text.

Have a look at http://jsfiddle.net/9BKD9/ for an example of the problem

![highstocks_label_example](https://f.cloud.github.com/assets/3628479/171163/31e09a08-7a8d-11e2-9d00-80d7a2664952.png)

Now the connecting line will start from the top of the label in this case.