Make DOMImplementation::hasFeature() behave according to specification

LayoutTests/svg/dynamic-updates/script-tests/SVGPolygonElement-svgdom-requiredFeatures.js

 // [Name] SVGPolygonElement-svgdom-requiredFeatures.js
 // [Expected rendering result] a series of PASS messages
 
 createSVGTestCase();
 
 var polygonElement = createSVGElement("polygon");
 polygonElement.setAttribute("points", "0,0 200,0 200,200 0, 200");
 
 rootSVGElement.appendChild(polygonElement);
 
 function repaintTest() {
     debug("Check that SVGPolygonElement is initially displayed");
     shouldBeEqualToString("document.defaultView.getComputedStyle(polygonElement, null).display", "inline");
     debug("Check that setting requiredFeatures to something invalid makes it not render");
-    polygonElement.requiredFeatures.appendItem("foo");
+    polygonElement.requiredFeatures.appendItem("http://www.w3.org/TR/SVG11/feature#BogusFeature");
     shouldBeEqualToString("document.defaultView.getComputedStyle(polygonElement, null).display", "");
     debug("Check that setting requiredFeatures to something valid makes it render again");
     polygonElement.requiredFeatures.replaceItem("http://www.w3.org/TR/SVG11/feature#Shape", 0);
     shouldBeEqualToString("document.defaultView.getComputedStyle(polygonElement, null).display", "inline");
     debug("Check that adding something valid to requiredFeatures keeps rendering the element");
     polygonElement.requiredFeatures.appendItem("http://www.w3.org/TR/SVG11/feature#Gradient");
     shouldBeEqualToString("document.defaultView.getComputedStyle(polygonElement, null).display", "inline");
     debug("Check that adding something invalid to requiredFeatures makes it not render");
-    polygonElement.requiredFeatures.appendItem("foo");
+    polygonElement.requiredFeatures.appendItem("http://www.w3.org/TR/SVG11/feature#BogusFeature");
     shouldBeEqualToString("document.defaultView.getComputedStyle(polygonElement, null).display", "");
 
     completeTest();
 }
 
 var successfullyParsed = true;