["BUGFIX" beta] Improve unhandled action error messages

1) The comment about `return true` being a possible source of error
   is incorrect; even if an action handler returns true, the action
   is considered handled and it won't cause an error even if parent
   routes don't handle the event.
2) 99% of the time, the only time people see the error about no
   active handlers is when they try to call `Route#send` within
   `model`, `beforeModel`, or `afterModel`. Most likely the solution
   is to call `Transition#send` on the transition object passed into
   the various model hooks, so I've updated the error message
   to suggest using `Transition#send` instead.
Updated the docs for Ember.Route.activate() to show that it happens on every enter, and not just the first time.
Merge pull request #3677 from SinisterMinister/master

Updated the docs for Ember.Route.activate()
Merge pull request #3656 from machty/better-action-errors

["BUGFIX" beta] Improve unhandled action error messages
Add tests to ensure EXTEND_PROTOYPES is honored.
Merge pull request #3678 from rjackson/fix_prototype_assertions

Add tests to ensure EXTEND_PROTOYPES is honored.
[BUGFIX beta] Allow test helpers to be injected on specific object.

This allows the test helpers to be injected into an object other than
`window`.
Merge pull request #3686 from rjackson/refactor_testing

[BUGFIX beta] Allow test helpers to be injected on specific object.
Remove inconsistent global reference to Handlebars in helper
Merge pull request #3688 from kumavis/master

Fix typo in Handlebars
Update for Handlebars 1.1
[DOC release] Add Ember.Application.testHelper documentation.
[FEATURE ember-testing-lazy-routing]

* `setupForTesting` sets the application into testing mode (which is
  used to defer readiness.
* Adds an initializer that defers readiness if the application is in
  testing mode.
* `visit` helper has been updated to advance readiness upon first call.
* `App.reset()` now behaves the same after `setupForTesting` (in a
  deferred state).
Merge pull request #3692 from rjackson/add_test_helpers_docs

[DOC release] Add Ember.Application.testHelper documentation.
Merge pull request #3695 from rjackson/defer_readiness_in_initializer

[FEATURE ember-testing-lazy-routing]
Renaming everyBy and anyBy to isEvery and isAny
Merge pull request #3662 from twokul/everyBy

Renaming everyBy and anyBy to isEvery and isAny
Support HANDLEBARS_PATH for Gemfile

This makes it easier for Ember's tests to be run against a
development version of Handlebars.
[DOC] Add ember-testing-lazy-routing to FEATURES.md.
Merge pull request #3697 from rjackson/add_docs_for_lazy_routing

[DOC] Add ember-testing-lazy-routing to FEATURES.md.