[OpenAFS] Cache file status after Network error

[Harald Barth]

> It is supposed to be the case that when a file becomes unreferenced
> (goes "inactive" in bsd parlance) that dirty data is thrown away on
> the grounds that it can only still be around due to a write error.We
> really should not invalidate the data any sooner than that, since
> existing mmaps/etc may be referring to it.

I think a write error should trigger the same invalidation as a
callback because that means that the data is not in sync with the data
on the server any more. Even if a file is open and referenced, 
a callback can arrive and invalidate. (insert disclaimer here :)

Harald.