Added test case for winding order of polygon rings. See mapnik/mapnik#2371 and mapbox/tilemill#2110.
Merge branch 'master' of https://github.com/IvanSanchez/mapnik

Conflicts:
	tests/visual_tests/images/polygon-winding-order-300-300-1.0-agg-reference.png
	tests/visual_tests/images/polygon-winding-order-300-300-1.0-cairo-reference.png
	tests/visual_tests/images/polygon-winding-order-300-300-2.0-agg-reference.png
	tests/visual_tests/images/polygon-winding-order-300-300-2.0-cairo-reference.png