Continuing Feature/record download info

I don't know if there's a better way to do this, but I'm continuing where @dstufft left off over in #453.

I've tried to address the concerns raised in the original (hardcoded paths and other test issues).

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. Here's a Travis CI build: http://travis-ci.org/#!/tgecho/pip/builds/1061109

The two test failures in 2.7/3.1/3.2 are for bundling, but I can't quite wrap my head around them yet. If someone with a better clue about pip internals could take a stab we'd be grateful.

There's another error in test_editable_git_upgrade in 2.5/2.6 that I'm not sure is related, but I'm looking at that. I'll also try to get a test on 2.4.