[NICETHING beta] Expose helpful vars in {{debugger}} helper body

Folk often don't know what to do within `{{debugger}}`.
This should give them a little more to work with.
[BUGFIX beta] contextualizeBindingPath should be aware of empty paths
Merge pull request #3870 from marcioj/3860_fix

contextualizeBindingPath should be aware of empty paths
Do not allow overwriting of controllers proxy properties

It was possible to accidentally set the value of `controllers.foo`, where
foo is a container-retrieved controller value as specified using `needs`.

There is no case where a developer would want to do this on purpose, and
it can cause confusion. This commit throws an error when this occurs.
render helper with context, now creates the controller
with its model, rather than setting the model post creation.

Setting the context post creating causes unneeded and wasteful change events.

@hjdivad & @stefanpenner
Merge pull request #3871 from lukemelia/read-only-needs

Do not allow overwriting of controllers proxy properties
remove Ember.alias as it has been deprecated since 2013-01-08
Merge pull request #3880 from stefanpenner/remove-ember-alias

remove Ember.alias as it has been deprecated since 2013-01-08
Merge pull request #3878 from stefanpenner/fix-render-helper

render helper with context, now creates the controller
Optimizes `{{#unbound if}}` and `{{#unbound unless}}`.

They no longer create useless metamorph views and generally execute
less code. There is no public API change here, just optimization.

Props to @machty for the review and help.
Merge pull request #3881 from lukemelia/unboundif

Optimizes `{{#unbound if}}` and `{{#unbound unless}}`.
Remove long deprecated Ember.Button
Merge pull request #3863 from rjackson/fix_publishing_of_builds

[BUGFIX beta] Update to the latest `ember-dev` and fix build publishing.
Merge pull request #3882 from selva-G/remove-emberbutton

Remove long deprecated Ember.button
Merge pull request #3854 from machty/better-debugger

[NICETHING beta] Expose helpful vars in {{debugger}} helper body
[DOC beta] Clarify context of a component's block.