python: 2.7.9rc1 devel

ensurepip is backported to 2.7.9; use that to get pip instead of staging pip and setuptools ourselves.
> the reason you have to uninstall pip is because you have a broken installation of pip where the metadata files indicate that pip is installed, but you no longer have the binaries files

Well, pip is importable but the scripts to invoke it no longer exist. AFAICT the easiest way to regenerate the pip script is to force a reinstallation of pip anyway. If we force a reinstallation of pip with ensurepip (which we can only do by removing ~all the pips~ first), the net effect is to risk downgrading pip.

(I mean, or maybe we just write `#{bin}/python -m pip "$@"` to `#{bin}/pip` and call it a day...?)