Do not fade-in scrollbars if scrollview node has been deleted
Build scrollview
Merge remote-tracking branch 'upstream/dev-master' into dev-master
Fill out more Y.Model tests to increase coverage of code branches.
Add unit tests for Model's `id` aliasing feature.

**Note:** This identifies several problem areas with Model's current
implementation of its `id` aliasing feature. These areas are identified
by the "BUG" code comments.

Issue #446
Merge branch 'model-id-tests' into dev-master