+ add check in test/configure for use_window, use_screen.
+ add configure-checks for getopt's variables, which may be declared
as different types on some Unix systems.
+ add check in test/configure for some legacy curses types of the
function pointer passed to tputs().
+ modify init_pair() to accept -1's for color value after
assume_default_colors() has been called (Debian #337905).
+ modify test/background.c, adding commmand-line options to demonstrate
assume_default_colors() and use_default_colors().