Message 160946 - Python tracker

Actually, I was planning on resetting everything, but I haven't gotten that to work yet. I can't figure out why (but I will!).

With the current patch, where things are not reset, the only test I had to change was test_path_importer_cache_empty_string. That change is in the attached -0 diff.

I can't decide which way I prefer it. I might add a parameter to control the behavior.