[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.
[beta] Replaces anonynoums functions with named ones
[DOC beta] Assert if template for {{render}} not found.

Added an assertion if the template name provided to `{{render}}` was not
found.

Two tests were previously not working properly, and have been fixed. They registered
templates as `"blog/post"`, which is never looked up with `{{render}}` (as any
slashes in the name are translated to a period before this lookup
happens).

Resolves #3926.
Assert if {{render}} is called with an unquoted name.

Eventually, `{{render}}` should be similar to `{{partial}}` where an
unquoted templateName is used to do bound parameter lookup.

This PR updates the tests to use quotes, and adds an assertion if an
unquoted param was provided.
add Ember.computed.sum
[DOC beta] Fix Ember.computed docs
Merge pull request #3968 from tricknotes/fix-computed-doc

[DOC beta] Fix Ember.computed docs
[DOC beta] Fix syntax highlight
Merge pull request #3969 from tricknotes/code-highlight

[DOC beta] Fix syntax highlight
Fixes typo in error method documentation.
Merge pull request #3974 from abrinkman/master

Fixes typo in method documentation.
Cleanup test using Ember.$.trim

`String#replace(/\s+/g, '')` is the same as `Ember.$.trim`.
To simplify test code, I rewrite with the latter.
[DOC beta] Fix code highlight and add missing YUIDoc markup
Merge pull request #3979 from tricknotes/cleanup-tests

Cleanup test using Ember.$.trim
Merge pull request #3980 from tricknotes/fix-docs

[DOC beta] Fix code highlight and add missing YUIDoc markup
[DOC beta] Fix YUIdoc method names
unbound helper supports bound helper static strings
[DOC beta] Fixes highlighting
[DOC beta] fixes for docs
[DOC beta] fixes formatting