feat(change_detection.ts): export PipeFactory

Closes angular#2245

Author: PatrickJS

modules/angular2/change_detection.ts

@@ -47,7 +47,7 @@ export {DynamicChangeDetector} from './src/change_detection/dynamic_change_detec
 export {ChangeDetectorRef} from './src/change_detection/change_detector_ref';
 export {PipeRegistry} from './src/change_detection/pipes/pipe_registry';
 export {uninitialized} from './src/change_detection/change_detection_util';
-export {WrappedValue, Pipe} from './src/change_detection/pipes/pipe';
+export {WrappedValue, Pipe, PipeFactory} from './src/change_detection/pipes/pipe';
 export {NullPipe, NullPipeFactory} from './src/change_detection/pipes/null_pipe';
 export {
  defaultPipes,