Icon for tag highway=milestone

I would like to add icon for tag highway=milestone. It is described on wiki page:
http://wiki.openstreetmap.org/wiki/Tag:highway%3Dmilestone

I added only icon without any changes to default style. That icon should be optional and used only with custom rendering styles. It is very useful for e.g. for firefighters.

That icon could be accessed by custom style like:

```
<renderingStyle name="milestone.render" depends="default" defaultColor="#f1eae4" version="1">
<point>
     <filter minzoom="10" icon="highway_milestone" tag="highway" value="milestone"/>
</point>
</renderingStyle>
```

As I know in default compiled map tags highway=milestone are not present. But it could be used (and it is used) in customary created maps.