More work on feature/record download info

Hey! I pushed forward on your pull request as far as I could. I've tried to address the concerns raised in the original (hardcoded paths and other test issues). I also merged in upstream develop. Here's a compare of the actual changes I've made: https://github.com/tgecho/pip/compare/488b29dec8655bc33b498fb8382a33465339bbd7...feature/record-download-info

I'm a little puzzled as to why the tests failed so spectacularly in python 3, but I started with replacing the iteritems() and the errors all seemed to go away. I still can't wrap my head around what is breaking with bundling, and there's another unrelated error in test_editable_git_upgrade (only in 2.5/2.6) that I don't get either.

Anyway, it's progress. If you don't have time to continue right now, I'll see what I can do. I figured I'd send the code to you first before stepping on your toes upstream. :)

http://travis-ci.org/#!/tgecho/pip/builds/1061109