Testcase for polygon rings winding order

This should clear up mapnik/mapnik#2371.

Expected result is two polygons (clockwise and counterclockwise) with two inner rings each (again, clockwise and counterclockwise):

The offset LineSymbolizer is there just to check that the winding order is taken into account when rendering lines. I'm not worrying about the artifacts right now.

![polygon-winding-order-300-300-1 0-cairo](https://cloud.githubusercontent.com/assets/1125786/4011974/cab4ec66-2a09-11e4-82ba-769eb2d8451d.png)