docs(core): replace angular2/angular2 with the right barrel import.

Related to #5710
Closes #5847

modules/angular2/src/core/change_detection/pipe_transform.ts

@@ -13,7 +13,7 @@
  * The `RepeatPipe` below repeats the value as many times as indicated by the first argument:
  *
  * ```
- * import {Pipe, PipeTransform} from 'angular2/angular2';
+ * import {Pipe, PipeTransform} from 'angular2/core';
  *
  * @Pipe({name: 'repeat'})
  * export class RepeatPipe implements PipeTransform {

modules/angular2/src/core/linker/interfaces.ts

@@ -243,7 +243,7 @@ export interface DoCheck { ngDoCheck(); }
  * the interval when the binding is destroyed or the countdown completes.
  *
  * ```
- * import {OnDestroy, Pipe, PipeTransform} from 'angular2/angular2'
+ * import {OnDestroy, Pipe, PipeTransform} from 'angular2/core'
  * @Pipe({name: 'countdown', pure: false})
  * class CountDown implements PipeTransform, OnDestroy {
  *   remainingTime:Number;

modules/angular2/src/core/metadata.ts

@@ -253,7 +253,7 @@ export interface ComponentFactory {
  * ### Example as TypeScript Decorator
  *
  * ```
- * import {Component, View} from "angular2/angular2";
+ * import {Component, View} from "angular2/core";
  *
  * @Component({...})
  * @View({...})
@@ -356,7 +356,7 @@ export interface AttributeFactory {
  * ### Example as TypeScript Decorator
  *
  * ```
- * import {Query, QueryList, Component} from "angular2/angular2";
+ * import {Query, QueryList, Component} from "angular2/core";
  *
  * @Component({...})
  * class MyComponent {

modules/angular2/src/core/platform_directives_and_pipes.ts

@@ -8,7 +8,7 @@ import {CONST_EXPR} from "angular2/src/facade/lang";
  * ### Example
  *
  * ```typescript
- * import {PLATFORM_DIRECTIVES} from 'angular2/angular2';
+ * import {PLATFORM_DIRECTIVES} from 'angular2/core';
  * import {OtherDirective} from './myDirectives';
  *
  * @Component({
@@ -34,7 +34,7 @@ export const PLATFORM_DIRECTIVES: OpaqueToken = CONST_EXPR(new OpaqueToken("Plat
  * ### Example
  *
  * ```typescript
- * import {PLATFORM_PIPES} from 'angular2/angular2';
+ * import {PLATFORM_PIPES} from 'angular2/core';
  * import {OtherPipe} from './myPipe';
  *
  * @Component({

modules/angular2/src/core/zone/ng_zone.ts

@@ -34,7 +34,8 @@ export class NgZoneError {
  *
  * ### Example ([live demo](http://plnkr.co/edit/lY9m8HLy7z06vDoUaSN2?p=preview))
  * ```
- * import {Component, View, NgIf, NgZone} from 'angular2/angular2';
+ * import {Component, View, NgZone} from 'angular2/core';
+ * import {NgIf} from 'angular2/common';
  *
  * @Component({
  *   selector: 'ng-zone-demo'.