Icon for tag emergency=fire_hydrant

I would like to add icon for tag emergency=fire_hydrant. It is described on wiki page:
http://wiki.openstreetmap.org/wiki/Tag:emergency%3Dfire_hydrant

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="fire_hydrant.render" depends="default" defaultColor="#f1eae4" version="1">
<point>
     <filter minzoom="10" icon="emergency_fire_hydrant" tag="emergency" value="fire_hydrant"/>
</point>
</renderingStyle>
```