[BUGFIX beta] Make setPath errors clearer.
Merge pull request #3951 from rjackson/make_set_errors_better

[BUGFIX beta] Make setPath errors clearer.
[FEATURE string-parameterize]
Extract has_element state to your own file
Merge pull request #3953 from gdub22/string-parameterize

[FEATURE string-parameterize]
Merge pull request #3954 from marcioj/extract_has_element

Extract has_element state to your own file
[beta] controller unit-testability: stubbable `controllers` property

Removed the `readOnly`-ness of the `controllers`
CP so that it could be stubbed out for unit tests.
Merge pull request #3956 from machty/stubbable-needs

[beta] controller unit-testability: stubbable `controllers` property
[beta] controller unit-testability: embrace read-only meta
Fix property name in code comment

The property name of `Ember.Array#hasArrayObservers` is incorrect.
Remove unexist param's comment

`Ember.Enumerable#enumerableContentDidChange` allow to be given two arguments.
* `removing`
* `adding`

Not contains `start`.
[beta] better docs for modelFor

I wanted to stress that its main utility was for
accessing models on parent routes rather than
giving the impression that it's useful/meaningful
for grabbing models from any ol route, even if
it's not in the current route hierarchy, which
doesn't really make sense, right?
[beta] Remove unused variable in test
Merge pull request #3959 from pangratz/cleanup_test

Remove unused variable in test
Merge pull request #3957 from tricknotes/fix-code-comment

Fix code comment
Merge pull request #3958 from machty/modelfor-doc

[beta] better docs for modelFor
Fix to highlight code in document
Merge pull request #3960 from tricknotes/fix-to-highlight-code-in-document

Fix to highlight code in document
[DOC beta] Fix ClassMixin.reopen docs.
[DOC beta] Fix CoreObject.toString docs.