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

Related to #5710
Closes #5847

modules/angular2/src/common/common_directives.ts

@@ -17,7 +17,7 @@ import {CORE_DIRECTIVES} from './directives';
  *
  * ```typescript
  * import {NgClass, NgIf, NgFor, NgSwitch, NgSwitchWhen, NgSwitchDefault, NgModel, NgForm} from
- * 'angular2/angular2';
+ * 'angular2/common';
  * import {OtherDirective} from './myDirectives';
  *
  * @Component({
@@ -33,7 +33,7 @@ import {CORE_DIRECTIVES} from './directives';
  * one could import all the common directives at once:
  *
  * ```typescript
- * import {COMMON_DIRECTIVES} from 'angular2/angular2';
+ * import {COMMON_DIRECTIVES} from 'angular2/common';
  * import {OtherDirective} from './myDirectives';
  *
  * @Component({
@@ -46,4 +46,4 @@ import {CORE_DIRECTIVES} from './directives';
  * }
  * ```
  */
-export const COMMON_DIRECTIVES: Type[][] = CONST_EXPR([CORE_DIRECTIVES, FORM_DIRECTIVES]);
+export const COMMON_DIRECTIVES: Type[][] = CONST_EXPR([CORE_DIRECTIVES, FORM_DIRECTIVES]);

modules/angular2/src/common/directives/core_directives.ts

@@ -17,7 +17,7 @@ import {NgSwitch, NgSwitchWhen, NgSwitchDefault} from './ng_switch';
  * Instead of writing:
  *
  * ```typescript
- * import {NgClass, NgIf, NgFor, NgSwitch, NgSwitchWhen, NgSwitchDefault} from 'angular2/angular2';
+ * import {NgClass, NgIf, NgFor, NgSwitch, NgSwitchWhen, NgSwitchDefault} from 'angular2/common';
  * import {OtherDirective} from './myDirectives';
  *
  * @Component({
@@ -32,7 +32,7 @@ import {NgSwitch, NgSwitchWhen, NgSwitchDefault} from './ng_switch';
  * one could import all the core directives at once:
  *
  * ```typescript
- * import {CORE_DIRECTIVES} from 'angular2/angular2';
+ * import {CORE_DIRECTIVES} from 'angular2/common';
  * import {OtherDirective} from './myDirectives';
  *
  * @Component({

modules/angular2/src/common/directives/ng_class.ts

@@ -31,7 +31,8 @@ import {StringMapWrapper, isListLikeIterable} from 'angular2/src/facade/collecti
  * ### Example ([live demo](http://plnkr.co/edit/a4YdtmWywhJ33uqfpPPn?p=preview)):
  *
  * ```
- * import {Component, NgClass} from 'angular2/angular2';
+ * import {Component} from 'angular2/core';
+ * import {NgClass} from 'angular2/common';
  *
  * @Component({
  *   selector: 'toggle-button',

modules/angular2/src/common/directives/ng_style.ts

@@ -23,7 +23,8 @@ import {isPresent, isBlank, print} from 'angular2/src/facade/lang';
  * ### Example ([live demo](http://plnkr.co/edit/YamGS6GkUh9GqWNQhCyM?p=preview)):
  *
  * ```
- * import {Component, NgStyle} from 'angular2/angular2';
+ * import {Component} from 'angular2/core';
+ * import {NgStyle} from 'angular2/common';
  *
  * @Component({
  *  selector: 'ngStyle-example',