ncurses 5.6 - patch 20080607

+ finish changes to wgetch(), making it switch as needed to the
  window's actual screen when calling wrefresh() and wgetnstr().  That
  allows wgetch() to get used concurrently in different threads with
  some minor restrictions, e.g., the application should not delete a
  window which is being used in a wgetch().
+ simplify mutex's, combining the window- and screen-mutex's.