Re: next-error-last-buffer

[Richard Stallman]

    This problem occurs when going through results in a grep buffer
    visits a patch file in diff mode.  The next call of `next-error'
    continues to visit places from a patch file, not from a grep buffer.

    To avoid this problem, the variable `next-error-function' could be set
    to nil in a buffer visited by the latest call of `next-error-function'.

This fix has a drawback; it will make that buffer permanently
incapable of being used as a series of references to places.

I think we should look for a way to disable this temporarily instead.
However, I am not sure how that would work--what would be the
condition on which to reenable this buffer's value of
next-error-function?