ncurses 6.1 - patch 20180630

+ add acsc string to vi200 (Nibby Nebbulous)
  add right/down-arrow to vi200's acsc -TD
+ add "x" to tput's getopt string so that "tput -x clear" works
  (Nicholas Marriott).
+ minor fixes prompted by anonymous report on stack overflow:
  + correct order of checks in _nc_get_locale(), for systems lacking
    locale support.
  + add "#error" in a few places to flag unsupported configurations