fix(router): don't prepend `/` unnecessarily to Location paths

Closes #6729
Closes #5502

modules/angular1_router/test/integration/navigation_spec.js

@@ -131,6 +131,26 @@ describe('navigation', function () {
     expect(elt.text()).toBe('outer { inner { one } }');
   });
 
+  it('should work when parent route has empty path', inject(function ($location) {
+    registerComponent('childCmp', {
+      template: '<div>inner { <div ng-outlet></div> }</div>',
+      $routeConfig: [
+        { path: '/b', component: 'oneCmp' }
+      ]
+    });
+
+    $router.config([
+      { path: '/...', component: 'childCmp' }
+    ]);
+    compile('<div>outer { <div ng-outlet></div> }</div>');
+
+    $router.navigateByUrl('/b');
+    $rootScope.$digest();
+
+    expect(elt.text()).toBe('outer { inner { one } }');
+    expect($location.path()).toBe('/b');
+  }));
+
 
   it('should work with recursive nested outlets', function () {
     registerDirective('recurCmp', {

modules/angular2/src/router/router.ts

@@ -438,7 +438,7 @@ export class RootRouter extends Router {
                   }
                   var emitPath = instruction.toUrlPath();
                   var emitQuery = instruction.toUrlQuery();
-                  if (emitPath.length > 0) {
+                  if (emitPath.length > 0 && emitPath[0] != '/') {
                     emitPath = '/' + emitPath;
                   }
 
@@ -465,7 +465,7 @@ export class RootRouter extends Router {
   commit(instruction: Instruction, _skipLocationChange: boolean = false): Promise<any> {
     var emitPath = instruction.toUrlPath();
     var emitQuery = instruction.toUrlQuery();
-    if (emitPath.length > 0) {
+    if (emitPath.length > 0 && emitPath[0] != '/') {
       emitPath = '/' + emitPath;
     }
     var promise = super.commit(instruction);

modules/angular2/test/router/integration/navigation_spec.ts

@@ -105,6 +105,20 @@ export function main() {
              });
        }));
 
+    it('should navigate to child routes when the root component has an empty path',
+       inject([AsyncTestCompleter, Location], (async, location) => {
+         compile(tcb, 'outer { <router-outlet></router-outlet> }')
+             .then((rtc) => {fixture = rtc})
+             .then((_) => rtr.config([new Route({path: '/...', component: ParentCmp})]))
+             .then((_) => rtr.navigateByUrl('/b'))
+             .then((_) => {
+               fixture.detectChanges();
+               expect(fixture.debugElement.nativeElement).toHaveText('outer { inner { hello } }');
+               expect(location.urlChanges).toEqual(['/b']);
+               async.done();
+             });
+       }));
+
     it('should navigate to child routes of async routes', inject([AsyncTestCompleter], (async) => {
          compile(tcb, 'outer { <router-outlet></router-outlet> }')
              .then((rtc) => {fixture = rtc})