[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