[BUGFIX release] `Ember.keys` should return own property

In IE8, `Ember.keys` couldn't return property that named the same as
own prototype property.
[BUGFIX release] Fix to return `undefined` for `href` of {{link-to}}

The old IE renders `false` to `href="false"` against my expectation.
[BUGFIX release] `Ember.Object.extend` should allow any prorerty
[BUGFIX beta] Don't use incompatible array methods

The old IE doesn't have some `Array` methods.
[BUGFIX beta] link-to, bound helper issues with arrays of primitives

/cc @kselden

Fixes #3342. Fixes #3429.