ecd67c8223
Using `exec -a` caused Python to use $PATH to look up the full program name (for `sys.executable`), which 314937d then tried to fix by changing $PATH also for the system version. This is not necessary anymore when not using the short name with `exec`. This was rejected upstream (https://github.com/rbenv/rbenv/pull/1089#issuecomment-394531896), since it is not a problem with Ruby apparently. Uses $PYENV_ROOT to check if system version is used. Fixes https://github.com/pyenv/pyenv/issues/98. Fixes https://github.com/pyenv/pyenv/issues/789.