fix(CSSClass): change selector to ng-class

BREAKING CHANGE:

The selector for the CSSClass directive was changed
from [class] to [ng-class]. The directive itself was
renamed from CSSClass to NgClass

Closes #3498

modules/angular2/src/directives/ng_class.ts

@@ -25,17 +25,17 @@ import {ListWrapper, StringMapWrapper, isListLikeIterable} from 'angular2/src/fa
  * # Example:
  *
  * ```
- * <div class="message" [class]="{error: errorCount > 0}">
+ * <div class="message" [ng-class]="{error: errorCount > 0}">
  *     Please check errors.
  * </div>
  * ```
  */
 @Directive({
-  selector: '[class]',
+  selector: '[ng-class]',
   lifecycle: [LifecycleEvent.onCheck, LifecycleEvent.onDestroy],
-  properties: ['rawClass: class']
+  properties: ['rawClass: ng-class']
 })
-export class CSSClass {
+export class NgClass {
   private _differ: any;
   private _mode: string;
   _rawClass;

modules/angular2/src/render/dom/compiler/compile_element.ts

@@ -19,7 +19,7 @@ export class CompileElement {
   // inherited down to children if they don't have an own elementBinder
   inheritedElementBinder: ElementBinderBuilder = null;
   compileChildren: boolean = true;
-  elementDescription: string;  // e.g. '<div [class]="foo">' : used to provide context in case of
+  elementDescription: string;  // e.g. '<div [title]="foo">' : used to provide context in case of
                                // error
 
   constructor(public element, compilationUnit: string = '') {