Recursive engine test

[ankrgyl]

I think we can run the qs tests against each supported engine, with the following algorithm:

1. Look at a qs file, and enumerate the list of imports
2. If there are no imports, then proceed
3. Otherwise, recursively process each import, and then replace it with an import from the database
4. Run the qs file, save it to the database, and remember that we've processed it (for future files that import it)