Trigger actions for keyUp and keyDown.

* Trigger `key-up` and `key-down` actions.
* Remove extraneous event listeners.
[DOC release] Array mixin cleanup
Prevent setting aliases on self
[BUGFIX release] make GUID_KEY = intern(GUID_KEY) actually work on ES3.

Ember.keys() filters out __ leading underscores so it returns undefined for GUID_KEY. This change not only works in ES3 browsers but is faster across all browsers I benchmarked.
Merge pull request #5612 from emberjs/fix-intern

[BUGFIX release] make GUID_KEY = intern(GUID_KEY) actually work on ES3.
Include keyName into the assertion error
Merge pull request #5608 from gtsop/master

Assert setting alias on self
[BUGFIX beta] ember-routing: Always inherit model from parent
Allow development only feature flags.

When a flag with `development-only` is found in `features.json` it will
be enabled (flags stripped) for `ember.js`, and disabled (flags
stripped) for `ember.prod.js`.
Fix argument order for handleMandatorySetter.
Use separate FEATURES for dev vs prod builds.
Use `ember-tests.prod.js` when testing prod builds.
[Bugfix Beta] Improve Ember.Map

* [Perf + ES6] no longer clone array before enumeration (dramatically reduce allocations)
* [Perf] Don’t rebind the callback of forEach if not needed
* [Perf + ES6] no longer allow Map#length to be bindable
* [Perf] don’t double guid keys, as they are passed from map to ordered set (add/remove)
* [ES6] deprecate Map#remove in-favor of the es6 Map#delete
* [ES6] error if callback is not a function
* [ES6] Map#set should return the map. This enables chaining map.`map.set(‘foo’,1).set(‘bar’,3);` etc
* [ES6] remove length in-favor of size.
* [ES6] throw if constructor is invoked without new
* [ES6] Make inheritance work correctly
Merge pull request #5532 from rwjblue/allow-production-only-feature-flags

Allow development only feature flags.
Merge pull request #5610 from ef4/always-inherit

Fix ember-routing-inherits-parent-model for nestable routes.
Test optional features in production builds.
[FEATURE ember-metal-injected-properties] Ensure tests work in prod builds.
Merge pull request #5618 from rwjblue/run-feature-tests-in-prod

Ensure optional features are tested against production builds.
Ensure only failing deprecations are logged by test helpers.
Add deprecations for Map.prototype.remove and Map.prototype.length.