ncurses 6.1 - patch 20180407

ncurses 6.1 - patch 20180407

+ clarify in manual pages that vwprintw and vwscanw are obsolete,
  not part of X/Open Curses since 2007.
+ use "const" in some prototypes rather than NCURSES_CONST where X/Open
  Curses was updated to do this, e.g., wscanw, newterm, the terminfo
  interface.  Also use "const" for consistency in the termcap
  interface, which was withdrawn by X/Open Curses in Issue 5 (2007).
  As of Issue 7, X/Open Curses still lacks "const" for certain return
  values, e.g., keyname().