Fixing 434 links in 111 files for pyenv

A.K.A. shell scripting is awesome, and why don’t-repeat-yourself (DRY) matters. Context: PyPy moved its repositories to Heptapod (unrelated, but I have to mention it is an awesome source-code forge and a project) and binary builds to downloads.python.org. PyPy could no longer be installed using pyenv. Since I happened to try install PyPy the same day it stopped working, I was among the few it noticed it.