bug#9780: sort -u throws out non-duplicates

[Paul Eggert]

On 08/17/2012 12:36 PM, Jim Meyering wrote:
> The first time the safe_text buffer is allocated
> it will have to be disjoint from the line.text buffer
> and from the buffer into which we're about to fread.
> Thereafter, regardless of reallocation, overlap should
> always be false.

I haven't thought it through entirely, but I was
worried about the case where there is a saved line
but no saved_text, the buffer is reallocated, and
then we test for overlap.  If the reallocated buffer
does not overlap the original buffer, the test for
overlap will fail even though the saved line needs
to be copied into a new saved_text buffer.

I'll stare at the code some more....