ncurses 5.6 - patch 20080503

ncurses 5.6 - patch 20080503

+ modify screen.* terminfo entries using new screen+fkeys to fix
  overridden keys in screen.rxvt (Debian #478094) -TD
+ modify internal interfaces to reduce wgetch()'s dependency on the
  global SP.
+ simplify some loops with macros each_screen(), each_window() and
  each_ripoff().
+ continue modifying test/ditto.c toward making it demonstrate
  multithreaded use_screen(), using fifos to pass data between screens.
+ fix typo in form.3x (report by Mike Gran).