ItemizedOverlay : margin of error for activate an item

```
It could be useful if we can indicate a margin of error for activating items in 
an ItemizedOverlay.

For example, if an item of 12x12 pixels is displayed, it is a little difficult 
to select it. It would be nice if a touch event catched near this item could 
activate it.
```

Original issue reported on code.google.com by `o.bou...@gmail.com` on 3 Dec 2010 at 7:46
