Got rid of the concept of test source modules, and instead just returned
the test source modules as seed files, so that TestPack now properly
conforms to the BundlableNode interface, and code like the bundle-deps
command can actually work when run over a TestPack instance.
Merge pull request #455 from BladeRunnerJS/allow-bundle-deps-command-to-work

Got rid of the concept of test source modules, and instead just returned