sort: support all combinations of -d, -f, -i, -R, and -V

sort: support all combinations of -d, -f, -i, -R, and -V

* NEWS: Document this.
* src/sort.c (getmonth): Omit LEN arg, as MONTH is now null-terminated.
(compare_random): Don't null-terminate keys, as caller now does that.
(compare_version): Remove.
(debug_key): Null-terminate string for getmonth.
(keycompare): Support combining -R with any of -d, -f, -i, -V.
Also, support combining -V with any of -d, -i.
(check_ordering_compatibility): Allow newly-supported combinations.
* tests/misc/sort (02q, 02r, 02s): New tests, for new combinations.
(incompat2): Now test -nR, since -fR are now compatible.