Next version of the sorter -- both presorting and unifying works.

Next version of the sorter -- both presorting and unifying works.

sort-test now does just `sort -u' and it's about 30% slower than its
GNU counterpart, probably due to extra copies of sorting keys by our
buffered I/O layer. Fortunately, a typical case will be long data with
short keys where we should be efficient as we can use bbcopy().