ncurses 6.0 - patch 20160507

+ amend change to _nc_do_color to restore the early return for the
  special case used in _nc_screen_wrap (report by Dick Streefland,
  cf: 20151017).
+ modify test/ncurses.c:
  + check return-value of putwin
  + correct ifdef which made the 'g' test's legend not reflect changes
    to keypad- and scroll-modes.
+ correct return-value of extended putwin (report by Mike Gran).