Fix documentation for cancel method of Ember.TextSupport
[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] `Ember.Object.extend` should allow any prorerty
Update documentation for "customEvents"

The "loadedmetadata" event is no longer considered a bubbling event, and subsequently it will never be triggered.
[BUGFIX beta] Don't use incompatible array methods

The old IE doesn't have some `Array` methods.
Merge pull request #3511 from kanongil/patch-1

Update documentation for "customEvents"
Merge pull request #3508 from tricknotes/fix-object-extend-for-old-ie

[BUGFIX release] Fix Ember.Object.extend for old IE
Merge pull request #3506 from tricknotes/fix-for-old-ie

[BUGFIX beta] Don't use incompatible array methods
Merge pull request #3504 from lackac/patch-1

Fix documentation for cancel method of Ember.TextSupport