Re: URL not following some 302 redirects after recent changes

[Richard Stallman]

      While a sentinel is running, the process sentinel is temporarily
    set to @code{nil} so that the sentinel won't run recursively.
    For this reason it is not possible for a sentinel to specify
    a new sentinel.

We did that to avoid a class of bugs.  But it has caused a new
problem.  So I am looking for a better solution.

Here's one idea.  Instead of setting the sentinel temporarily to nil,
set it temporarily to `sentinel-temporarily-inhibited'.  That would be
ignored just as nil is ignored.

On restoring the sentinel, if its current value isn't
`sentinel-temporarily-inhibited', just discard the old value instead
of restoring it.

This would prevent recursion just like the current code, but sentinels
that set the sentinel would work once again.

Does anyone see a problem with this fix?