curses ">>" (terse "--More--")

I've noticed many instances of the game pausing and not being sure why,
then pressing <space> and having it resume.  The curses interface had
a tendency to put its equivalent of the --More-- prompt, >>, somewhere
where that wasn't visible, either off the right hand edge (possibly) or
underneath the window borders if those were enabled.  Especially the
very last one it issues prior to exit.  (An extra one compared to tty
behavior.)

This ended up being a pretty substantial overhaul of message window
handling.  I wouldn't be surprised if it has off-by-one errors which
happen to be paired up and cancel each other out.  ">>" is still drawn
in orange if guicolor is on, now in inverse video when that is off.
If it happens to be drawn at the same screen location in consecutive
instances, the first ">" will toggle between blink and not blink so
that there'll be no doubt as to whether the keypress registered when
dismissing it (moot if the text preceding it is different but there's
no attempt to be smart enough to check that, just screen placement).

include/wincurs.h

@@ -213,6 +213,7 @@ extern void curses_cleanup(void);
 /* cursmesg.c */
 
 extern void curses_message_win_puts(const char *message, boolean recursed);
+extern void curses_got_input(void);
 extern int curses_block(boolean require_tab); /* for MSGTYPE=STOP */
 extern int curses_more(void);
 extern void curses_clear_unhighlight_message_window(void);