Address concerns with injected properties feature

This addresses issues raised in the comments of #5162.

- [ ] [remove unnecessary `hasOwnProperty` check](https://github.com/emberjs/ember.js/pull/5162#discussion_r20398478)
- [ ] [make `lazyInjections` private](https://github.com/emberjs/ember.js/pull/5162#discussion_r20398493)
- [x] [remove unnecessary closure in `InjectedProperty` func](https://github.com/emberjs/ember.js/pull/5162#discussion_r20398539)
- [x] [name anonymous functions for better debugging](https://github.com/emberjs/ember.js/pull/5162#discussion_r20398547)
- [x] [remove injection type validation from production builds entirely](https://github.com/emberjs/ember.js/pull/5162#discussion_r20398647)
- [x] [added `onLookup` factory hook](https://github.com/emberjs/ember.js/pull/5162#issuecomment-63155654)
- [x] [cache lazy lookup validation](https://github.com/emberjs/ember.js/pull/5162#issuecomment-64290852)

I haven't addressed the top two concerns yet because I'm still uncertain of how the container should be treated within Ember. I'm also not 100% sure about the `onLookup` API, e.g. whether it should be a hook or a callback mechanism.
I like the idea of adding `onLookup`/`onLookupFactory` to the container and avoid potential clashes on `Ember.Object`s, but where would it get called? In `extend`? I can't think of a reasonable way to introspect the full container key at the time of extend.

Tom mentioned underscoring the hook to prevent clobbering, but that just makes me thing that hooks are the wrong approach altogether.

It would be even more awesome if both the dev-only type validation and the lazy injection validation could be accomplished through `onLookup`/`onLookupFactory` container methods, which would remove the need for the `lazyInjections` hook as well. I think the later could work as long as `onLookup` is only called on first instantiation (using the existing cache), but again there's the problem of not knowing the full container key of the factory being looked up.