[Bugfix] LazyGet of aliasDescriptor should respected the aliased...

... cache preference.

- [ ] WIP
- [x] write test
- [x] get feedback on approach.
- [x]  https://github.com/emberjs/ember.js/blob/master/packages/ember-metal/lib/computed.js#L504 should be also be aware of this.
- [ ] alias('foo.baz') where foo.baz is another descriptor
- [ ] audit other places that reach into meta (like array/reduce computed)
- [ ] add a test for lengthy alias chains
- [ ] Ember.lazyGet

add explicit tests for:
- [ ] Descriptor.prototype.getCache (include UNDEFINED case)
- [ ] Descriptor.prototype.lazyGet
- [ ] Descriptor.prototype.isCacheable