remove deprecated function (prepare 1.0)
FIX: A grouped #each with no content would raise errors.
FIX: You can change a grouped #each's content right before destroying it.
Inform about the Ember Inspector if not installed
invalid Controller#controllers accesses throw runtime exceptions

if controllers property was accessed, but the
controller being requested was not specified in
needs, we throw.
Controller#controllers property should be readOnly
Merge pull request #3254 from eviltrout/group_fixes

Fixes to GroupedEach
Merge pull request #3277 from stefanpenner/strict_needs

Strict Controller#needs
Merge pull request #3237 from sly7-7/evented-cleanup

remove deprecated function (prepare 1.0)
Merge pull request #3276 from teddyzeenny/extension-notification

Inform about the Ember Inspector if not installed
Slightly less forceful message for Ember Inspector
remove un-needed double assertion, and improve assertion message
Pull Controller#controllers CP Kick into init.