Reported by jeremyhetzler: with recently revised curses interface,
when dismissing a menu or prompt with ESC the screen flashed.
This was caused by calling beep() when the terminal is set for
'visible bell' (of flagged as incapable of 'audible bell'); the
curses library flashed the screen deliberately. We don't want that.
Change the function key handling to not call beep() when an ESC
is typed by itself rather than being the leading part of a
multi-character escape sequence. beep() will still be called if
you type an arrow key (or other function key) when nethack is
expecting text input. That's what the recent change intended.
This also removes an early return from parse_escape_sequence()
when a number pad key generates an escape sequence. I don't have
a number pad to verify that this bit works as intended.
Closes#1002
f5d400be75