Thanks for this patch. I've reviewed it and it looks good.
I'm concerned that it creates backward-incompatible behavior (namely, on Python 3.3 now including directories previously unspecified). I'm wishing we had added this behavior prior to the release of 3.3... in which case there was no compatibility to maintain :)
Alas, we weren't in a position to do that.
I think we will have to release this as a 4.0 release. I'll probably make a release containing only this change for clarity.