ncurses 6.2 - patch 20210828

ncurses 6.2 - patch 20210828

+ correct reversed check for --disable-root-environ (report/analysis
  by Arnav Singh, cf: 20210626).
+ apply gcc format attribute to prototypes which use a va_list
  parameter rather than a "..." variable-length parameter list
  (prompted by discussion in a tmux pull-request).
+ modify configure scripts to filter out redefinitions of _XOPEN_SOURCE,
  e.g., for NetBSD which generally supports 500, but 600 is needed for
  ncursesw.
+ improve documentation for tparm and static/dynamic variables.
+ improve typography in terminfo.5 (patch by Branden Robinson).