The "install everything" approach is OK for Windows and virtual
environments. The challenge is the shared bin directories on *nix systems.

Perhaps pip itself could be updated such that it installs the bare "pip"
only if sys.executable matches shutil.which("python")? At the very least,
ensurepip should work that way, but setuptools actually has the same
problem with respect to easy_install.

Also, if we do the temp directory workaround then we need to copy and then
delete the original rather than move (otherwise the file context will be
wrong under SELinux)