ncurses 5.6 - patch 20080531

+ modify wgetch() to use the screen which corresponds to its window
  parameter rather than relying on SP; some dependent functions still
  use SP internally.
+ factor out most use of SP in lib_mouse.c, using parameter.
+ add internal _nc_keyname(), replacing keyname() to associate with a
  particular SCREEN rather than the global SP.
+ add internal _nc_unctrl(), replacing unctrl() to associate with a
  particular SCREEN rather than the global SP.
+ add internal _nc_tracemouse(), replacing _tracemouse() to eliminate
  its associated global buffer _nc_globals.tracemse_buf now in SCREEN.
+ add internal _nc_tracechar(), replacing _tracechar() to use SCREEN in
  preference to the global _nc_globals.tracechr_buf buffer.