Treat the trailing newline as part of the line, as required by POSIX.2.

Treat the trailing newline as part of the line, as required by POSIX.2.

(struct line, findlines, compare, checkfp, mergefps, sort):
A line now includes its trailing newline.
(findlines): Do not replace newline with NUL.
(memcoll, keycompare): Work even if the data to be compared are
adjacent strings; this is possible now that lines contain the
trailing newline.
(fillbuf): Always have an unused byte at the end of the	buffer,
since memcoll and keycompare want to modify a byte after the last line.
(sortalloc, mergealloc): Increase by 1, for trailing byte.