WIP: Start using the ddmd frontend to more narrowly scope imports

[I just modified the ddmd frontend to dump all imported symbols](https://gist.github.com/joakim-noah/09cf49bee3d82b03a54f), based on [Daniel's newmagic ddmd branch from a couple weeks back](https://github.com/yebblies/dmd/tree/newmagic).  I was able to make these small cleanups by using the output from the resulting automated tool, doing more soon.

I'm posting this PR early so that it can be looked over as I go, and run through the auto-tester.