Nicer looking dead ends and turning circles for roads

This adds some nicer dead ends for roads.
Vehicles spawn on them in a random angle (0°, 90°, 180° or 270°).
The names of the dead ends are road_end_north, road_end_south, road_end_west and road_end_east.
Inclusion into the (over)map generator has been done.

Included in the PR are also some simple fixes to weird road alignment issues near rivers and bridges which existed previously. Now *most* roads should align properly to bridges.

There are two variations of dead ends: simple and turning circles. Sidewalks may apply, but turning circles may only appear in cities/next to sidewalks. But pictures say more than 1000 words:
![dead_end1](https://cloud.githubusercontent.com/assets/1675853/2562719/92f2da3c-b85c-11e3-9866-acfc61f5fe40.png)
![dead_end2](https://cloud.githubusercontent.com/assets/1675853/2562720/98d6ac26-b85c-11e3-9f80-e8aadc3dd280.png)
![dead_end_3](https://cloud.githubusercontent.com/assets/1675853/2562722/9aed7b5c-b85c-11e3-9458-3f7ae9142754.png)