Add source map support for Node tests

`gulp build-node-dev` now adds inline source maps. With the help of
`source-map-support`, the test errors now point to the correct line in
the untransformed source code.
Revert dag test cases.

The test cases couldn't actually pass, because we were renaming the
async methods to `gen_*`. Currently the tests only test the sync method.
We should add tests for the async method as well.

I added a test for `delegateToWorker` to make sure it returns a promise
and handles it correctly. This only tests the functionality in Node
though. We have to get the tests working in the browser as well.

I will add additional tests for the transform to ensure that it works as
intended.