Draw covered/underground lines beneath areas

(closes #4718)

test/spec/osm/way.js

@@ -234,6 +234,10 @@ describe('iD.osmWay', function() {
             expect(iD.Way({tags: { location: 'overground' }}).layer()).to.equal(1);
         });
 
+        it('returns -1 for covered=yes', function() {
+            expect(iD.Way({tags: { covered: 'yes' }}).layer()).to.equal(-1);
+        });
+
         it('returns -1 for location=underground', function() {
             expect(iD.Way({tags: { location: 'underground' }}).layer()).to.equal(-1);
         });

test/spec/svg/lines.js

@@ -90,8 +90,8 @@ describe('iD.svgLines', function () {
             iD.osmNode({id: 'b', loc: [1, 1]}),
             iD.osmNode({id: 'c', loc: [0, 0]}),
             iD.osmNode({id: 'd', loc: [1, 1]}),
-            iD.osmWay({id: 'lo', tags: {highway: 'residential', tunnel: 'yes'}, nodes: ['a', 'b']}),
-            iD.osmWay({id: 'hi', tags: {highway: 'residential', bridge: 'yes'}, nodes: ['c', 'd']})
+            iD.osmWay({id: 'lo', tags: {highway: 'residential', layer: '0'}, nodes: ['a', 'b']}),
+            iD.osmWay({id: 'hi', tags: {highway: 'residential', layer: '1'}, nodes: ['c', 'd']})
         ]);
 
         it('stacks higher lines above lower ones in a single render', function () {

test/spec/svg/osm.js

@@ -8,11 +8,12 @@ describe('iD.svgOsm', function () {
     it('creates default osm layers', function () {
         container.call(iD.svgOsm());
         var layers = container.selectAll('g.layer-osm').nodes();
-        expect(layers.length).to.eql(4);
-        expect(d3.select(layers[0]).classed('layer-areas')).to.be.true;
-        expect(d3.select(layers[1]).classed('layer-lines')).to.be.true;
-        expect(d3.select(layers[2]).classed('layer-points')).to.be.true;
-        expect(d3.select(layers[3]).classed('layer-labels')).to.be.true;
+        expect(layers.length).to.eql(5);
+        expect(d3.select(layers[0]).classed('layer-covered')).to.be.true;
+        expect(d3.select(layers[1]).classed('layer-areas')).to.be.true;
+        expect(d3.select(layers[2]).classed('layer-lines')).to.be.true;
+        expect(d3.select(layers[3]).classed('layer-points')).to.be.true;
+        expect(d3.select(layers[4]).classed('layer-labels')).to.be.true;
     });
 
     it('creates default osm point layers', function () {