added $setDirty method to INgModelController (added in v1.3.15+)

For Angular version 1.3.15+ INgModelController brings $setDirty method.

angularjs/angular.d.ts

@@ -474,6 +474,7 @@ declare module angular {
         // types do work and it's common to use them.
         $setViewValue(value: any, trigger?: string): void;
         $setPristine(): void;
+        $setDirty(): void;
         $validate(): void;
         $setTouched(): void;
         $setUntouched(): void;