[BUGFIX release] Fix #3681.

`Em.arrayComputed` is not presently compatible with lazy CPs. There are a few
issues.

1.  To keep refs up to date, observers stay around as long as the object does.
2.  Those observers can repopulate the cache, but when they do so they fail to
    add dependent keys when the cache was empty.

This commit works around 2. by not removing them in the first place.
Essentially the semantics for `ArrayComputedProperty`s differ from standard
`ComputedProperty`s with regards to laziness.

These observers need to be managed better.  Probably the right thing to do, now
that `recomputeOnce` is no longer necessary, is to:
  1. Fix `Em.computed.sort` to not use `recomputeOnce`;
  2. Fix `Em.arrayComputed` to return a proxy to the cached value;
  3. Teardown array observers when the deps count hits 0.

This will give reduce computed properties semantics much closer to regular
computed properties.  There are two important points to note about this
suggestion:

1.  The cached values would still update synchronously.  This can be improved
    with a lazy array implementation and @wycats's skiplist strategy.
2.  The semantics of an array computed would change such that existing refs
    would only be kept up to date as long as the cache had not been invalidated.
    This is probably fine: the current behaviour is not promised in the
    documentation anywhere and it would be pretty bad practice to keep
    references around rather than `Ember.get`ing them.
[BUGFIX beta] preserve base URL when using history location for routing
add Ember.computed.sum
revert 93a911be370fd6d995badb5e58c6b725a8277ca1

Ember.run.proxy will return as Ember.run.bind
Merge pull request #3707 from hjdivad/fix-3681

[BUGFIX beta] Fix #3681.
[Feature ember-metal-run-bind]
[DOC] Fix invalid syntax for classNames property in link-to helper

Trying to use array syntax throws `TypeError: this.classNames is undefined`
when rendering.
Merge pull request #4055 from praxxis/fix_link-to_classnames

[DOC] Fix invalid syntax for classNames property in link-to helper
[DOC] Move `actions` hash docs to ActionHandler mixin
[BUGFIX beta] Fix feature flagged tests.

Updates `ember-dev` to resolve an issue introduced with
https://github.com/emberjs/ember.js/pull/4045 that caused the test
harness to always ignore feature flagged tests.
Merge pull request #4057 from rjackson/fix_feature_flagged_tests

[BUGFIX beta] Fix feature flagged tests.
[BUGFIX beta] replaceURL checks of URL has actually changed

Fixes #4054
[BUGFIX beta] with-controller has parentController

Closes #4050
Merge pull request #4058 from bradfol/actions-docs

[DOC] Move `actions` hash docs to ActionHandler mixin
[BUGFIX][QueryParams] - Support for empty string QPs

This PR actually only adds tests to verify a fix
made in the route-recognizer. It should fix this bug:
https://github.com/emberjs/ember.js/issues/4054

This PR depends on: https://github.com/tildeio/route-recognizer/pull/19

That above PR changes the how QPs are parsed so that

`route/?foo` => `{ foo: true }`
and
`route/?foo=` => `{foo: ''}`
Enable features selected for next beta cycle.

The following features have been selected by the core team as being
ready to go for the next beta cycle. As such, they should be enabled on
all canary builds to ensure they are stable.

See https://github.com/emberjs/ember.js/issues/4052 for details.
Merge pull request #4061 from rjackson/enabled_goed_features

Enable features selected for next beta cycle.
Merge pull request #3949 from fivetanley/computed-sum-macro

add Ember.computed.sum
[DOC beta] connectOutlet expect a view instance. Updated docs to reflect it
Merge pull request #4060 from raytiley/qp-string

[BUGFIX][QueryParams] - Support for empty string QPs