feat(forms): Export NumberValueAccessor

Export `NumberValueAccessor` from `forms/directives.ts`

modules/angular2/src/core/forms/directives.ts

@@ -18,19 +18,20 @@ import {RequiredValidator, MinLengthValidator, MaxLengthValidator} from './direc
 export {NgControlName} from './directives/ng_control_name';
 export {NgFormControl} from './directives/ng_form_control';
 export {NgModel} from './directives/ng_model';
-export {NgControl} from './directives/ng_control';
 export {NgControlGroup} from './directives/ng_control_group';
 export {NgFormModel} from './directives/ng_form_model';
 export {NgForm} from './directives/ng_form';
-export {ControlValueAccessor} from './directives/control_value_accessor';
 export {DefaultValueAccessor} from './directives/default_value_accessor';
 export {CheckboxControlValueAccessor} from './directives/checkbox_value_accessor';
+export {NumberValueAccessor} from './directives/number_value_accessor';
+export {NgControlStatus} from './directives/ng_control_status';
 export {
   SelectControlValueAccessor,
   NgSelectOption
 } from './directives/select_control_value_accessor';
 export {RequiredValidator, MinLengthValidator, MaxLengthValidator} from './directives/validators';
-export {NgControlStatus} from './directives/ng_control_status';
+export {NgControl} from './directives/ng_control';
+export {ControlValueAccessor} from './directives/control_value_accessor';
 
 /**
  *