Bug in rplot.GeomDensity2D
I think line 567 in tools/rplot.py "ax.contour(Z, extent=[x_min, x_max, y_min, y_max])" should be changed to "ax.contour(Z.T, extent=[x_min, x_max, y_min, y_max])"

When I plot a density map, the graph is rotated by 90 degrees. 
