Partially revert "drop unnecessary requests.get allow_redirects=True kwarg"

...specifically, keeps it just for requests.head, which is the one http method where requests defaults it to off.
http://docs.python-requests.org/en/latest/user/quickstart/#redirection-and-history

thanks for noticing this @kylewm!

This (partially) reverts commit 2d0158597fce23c390742e5bac2631a87bee7acd.