Do not render link roads until z11

[matthijsmelissen]

This improves rendering on mid zoom levels by smoothing up the highways.

[matkoniecz]

I worry a bit about big T shaped junctions causing problems like hotosm/HDM-CartoCSS#236

Is it possible that in some places on Z10 motorways or trunks will appear disjointed after hiding link roads?

[matthijsmelissen]

There will be tiny gaps, like you can see on HOT: http://www.openstreetmap.org/?#map=10/50.0077/20.1551&layers=H
I think the gaps are so small on z10 that they are preferable over the strange bumps on the roads we have now: http://www.openstreetmap.org/?#map=10/51.5087/4.5133

[matthijsmelissen]

Can somebody please review this? I really dislike the effect the link roads currently produce.

[pnorman]

I'd prefer z10, but am okay with trying z11.