+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.
+