[BUGFIX beta] Handle beta branch builds properly.

The initial implementation of the `FORCE_BRANCH` flag did not
properly account for all scenarios.  This attempts to fix an
issue with builds of commits pushed directly to the beta/stable
branches.
Merge pull request #3891 from rjackson/update_ember-dev

[BUGFIX beta] Handle beta branch builds properly.
Upgrade RSVP

- instrumentation hooks for tooling
- still promise/a+ 2.0.2 compliant
- adds support for finally/catch
- adds documuncation
- perf
- cleanup
- several fixes
- no longer brings it's own async, as we just use the run-loop
Account for Ember.Test not being present
update docs
Merge pull request #3830 from stefanpenner/upgrade-rsvp

Upgrade RSVP
Allow `this` (global scope) to be null during module initialization

This is in preparation for ES6ifying things at some point.
Merge pull request #3846 from joliss/this

Allow `this` (global scope) to be null during module initialization
Come back test for `Ember.inspect`

This test was lost on #3883 .
Merge pull request #3895 from tricknotes/test-for-ember-inspect

Come back test for `Ember.inspect`