update backburner

included updated documentation for the run loop as well
DRY up container tests.
Fixes #4201
[DOC] Minor doc fix
Merge pull request #4247 from twokul/triggerAction-doc

[DOC] Minor doc fix
[FEATURE ember-metal-computed-empty-array]

Make `Em.computed.empty` respect arrays automatically, without users having to
know to use `array.[]`.
[FEATURE ember-handlebars-log-primitives]
Merge pull request #4252 from mmun/log-primitives

[FEATURE ember-handlebars-log-primitives]
[BUGFIX beta] Make Ember.RenderBuffer#addClass work as expected.
[DOC beta] Fix in controllerName comment
Merge pull request #4254 from MajorBreakfast/patch-3

Fix in controllerName comment
[FEATURE ember-eager-url-update] non a-tags work

Eager url updating was breaking for non a tags 
since their hrefs weren't being generated.

Thanks @jonnii for pointing this out
Merge pull request #4256 from machty/eager-non-a-tag

[FEATURE ember-eager-url-update] non a-tags work
Lazily setup observers for attributeBindings without defined values
Define HTML5 fields on input fields.

Previously, binding to this many attributes unnecessarily added a
significant performance penalty. Now these bindings are setup lazily for
values that were not previously defined on the instance.
[FEATURE ember-routing-auto-location] Adds better documentation for AutoLocation
Merge pull request #4258 from jayphelps/auto-location-documentation

[FEATURE ember-routing-auto-location] Adds better documentation for AutoLocation
[FEATURE query-params-new] Don't eagerly init controllers

This uses the somewhat hacky approach of looking up
a controller class's proto() to read its queryParams
configuration without instantiating it (unless it's
already been instantiated).

/cc @stefanpenner @ebryn
Merge pull request #4261 from machty/non-eager-init

[FEATURE query-params-new] Don't eagerly init controllers
[FEATURE query-params-new] Fix null QP check in transitionTo

redirecting with a null model was hitting some breaking
code with QP flags enabled.