Yelp/venv-update — pull request #19 by bukzor (2014-12-09 20:56:04+00:00)
Title: all fast

This gives us all the speedups we wanted.
I get ~6 seconds for a noop build in yelpmain, and 26s for a rebuild-from-cache.

I'm sorry the patch is so big.
I made a couple false starts, and removed a good amount of code that was added in the intermediate commits.
I've left them in the history however because they were generally correct and might prove useful in future.