bug#39389: 27.0.60; A couple of bugs messing with minibuffer completion of /sudo::

[Jimmy Yuen Ho Wong]

The problem, as I suspected in the very beginning, it's something within
`auth-source`. Specifically, it's the `insert-file-contents` call inside
`auth-source-netrc-parse` that locks up after having a dot prepended to
PATH, exec'ing shell, setting Emacs's env and exec-path. I'm at a lost
at how to debug this 1100-line function.