ncursesw portability

[kaduk@mit.edu]

Some systems (e.g., FreeBSD) provide the ncursesw function prototypes in the regular ncurses headers, e.g., curses.h and panel.h as used in owl.h, and curses.h in tester.c. configure should check for these ncursesw function declarations in headers as <curses.h> and <panel.h> as well as the current use of <ncursesw/curses.h> and <ncursesw/panel.h> (and modify the source accordingly).