Fix issue with unit tests and add `addToContext` helper

This PR does a few things:

* Fixes issue with jasmine
* Fixes broken unit test for `@contextDump`
* Updates the `coerce` private function (in dust-helpers.js) to be more consistent w/ coercion for various values. There's not a major loss in perf for what we're gaining in coercion support.
* Adds an addToContext helper which will capture the body of the helper and add the results to the current context using a name that's passed in as a parameter. It will optionally try to coerce the value to a type passed via a type parameter.