different rendering for aerialway=goods

This fixes #875.

new -top, old - bottom

![aerialway_new](https://cloud.githubusercontent.com/assets/3531092/3945346/af195540-263b-11e4-8a5b-a9d541593fde.png)
![aerialway_old](https://cloud.githubusercontent.com/assets/3531092/3945347/af9d3cac-263b-11e4-96b9-a066740604ab.png)

Since I did not find any source images for the aerialway polygon-line-pattern files I created new ones and put them in "symbols/src". Maybe you can point me towards different best practices if there are any.

I'm still having an anti-aliasing issue when moving from SVG to PNG, maybe you have some ideas to solve it without drawing a pixel-by-pixel circle.