bug#14804: Gnus spelling fix: unexist -> nonexistent

[Wolfgang Jenkner]

On Sun, Jul 07 2013, Paul Eggert wrote:

>> it's probably "non-existent" or "unexisting".
>
> Those are both English words, but "unexisting" is rare nowadays
> (almost obsolete), and "unexist" itself is not English.

Searching the web, however, suggests that, e.g., "make it unexist" is
quite commonly used, even where the context otherwise indicates that
people care about language usage.

Wolfgang