Import keys, and bring back Ember.keys tests lost in shuffle.

These tests were deleted in https://github.com/emberjs/ember.js/pull/5411.

Conflicts:
	packages/ember-metal/tests/keys_test.js
don't try and set rootURL on a string
fix failing test on IE11.

turns out the internal escaping stragety can differ between browsers. We
should defer to the browsers defaults
Fix then, than comment typo
Improve wording of documentation for getProperties()
[BUGFIX beta] Do not use defineProperty on each View instance.
Cleanup platform

Conflicts:
	packages/ember-metal/tests/properties_test.js
speedup watchKey by preventing for in related deopt

keyName in obj if obj is not really enumerable or a complex object causes the entire function to deopt. As MANDATORY_SETTER is only a development thing, in production we don’t want it’s guard deopting us.

Someday this whole block should be stripped for production builds
Fixes the function name

Related to this [PR](https://github.com/emberjs/ember.js/pull/5513).
Change ENV.MANDATORY_SETTER to FEATURES so it can be compiled out of production builds.
Revert inadvertent Brocfile changes.

Changes were made in cc39229.
[DOC] add example to computed properties set in API
More ES3 fixes.

Still need to conditionally switch on browsers that do not have ES5 compliant accessors, because isEnabled is compiled out based on development vs production build.
[DOC] Small grammar fix on enumerable filter method
[DOC release] fixed spelling error in dag.js docs
removed hyperlink from 'see' in README.md
[BUGFIX beta] Object.create(null) in Ember.inspect

This commit resolves an issue where objects passed to Ember.inspect that
contained an `Object.create(null)` object as a property would cause an
exception to be thrown.

I hit this in my app because we were `Ember.inspect`ing objects (a model
in this case) that had their container property set. The container’s
registry as of 1.8.0 is (you guessed it) an object with a null prototype.
[DOC] Fix example code syntax in code comment