Teach XHR how to handle relative urls.

sky/tests/services/xhr-relative.sky

Index: sky/tests/services/xhr-relative.sky
diff --git a/sky/tests/services/xhr.sky b/sky/tests/services/xhr-relative.sky
similarity index 52%
copy from sky/tests/services/xhr.sky
copy to sky/tests/services/xhr-relative.sky
index 7d5089b459dedd27c96b40076eb754773e229b3a..ef46a110deeaadcb0a840bec0c20d9811e766d43 100644
--- a/sky/tests/services/xhr.sky
+++ b/sky/tests/services/xhr-relative.sky
@@ -6,18 +6,15 @@
 describe('XMLHttpRequest', function() {
   this.enableTimeouts(false);
 
-  it('should be able to fetch text files', function(done) {
+  it('should be able to fetch relative urls', function(done) {
 
     var xhr = new XMLHttpRequest();
     xhr.onload = function() {
-      assert.equal(xhr.responseText, "This is data from the network.\n");
+      // Also testing that "this" is set correctly in the onload callback.
+      assert.equal(this.responseText, "This is data from the network.\n");
       done();
     };
-    xhr.onerror = function(error) {
-      assert.ok(false, "Got error: " + JSON.stringify(error));
-      done();
-    };
-    xhr.open("GET", "http://127.0.0.1:8000/sky/tests/services/resources/pass.txt");
+    xhr.open("GET", "resources/pass.txt");
     xhr.send();
   });
 });