'urgent' messages

Follow up on some old groundwork.  For tty, if the core has designated
a message as 'urgent', override any message suppression taking place
because of ESC typed at the --More-- prompt.  Right now, "You die"
messages, feedback about having something stolen, feedback for
"amorous demon" interaction (mainly in case of armor removal), and
exploding a bag of holding are treated as urgent.

The "You die" case is already handled by a hack in top-line handling;
I left that in place so the conversion of 3 or 4 pline("You die.*")
to custompline(URGENT_MESSAGE, "You die.*") was redundant.  There
are probably various non-You_die messages which precede done() which
should be marked urgent too.

Other interfaces might want to do something similar.  And we ought to
implement MSGTYPE=force or MSGTYPE=urgent to allow players to indicate
other messages that they want have to override suppression.  But I'm
not intending to work on either of those.  I mainly wanted to force
the magic bag explosion message to be shown since a sequence of "You
put <foo> into <bag>." messages is a likely candidate for --More--ESC.

win/tty/topl.c

@@ -582,8 +582,9 @@ msghistory_snapshot(boolean purge) /* clear message history buffer
 
 /* release memory allocated to message history snapshot */
 static void
-free_msghistory_snapshot(boolean purged) /* True: took history's pointers,
-                                            False: just cloned them */
+free_msghistory_snapshot(
+    boolean purged) /* True: took history's pointers,
+                     * False: just cloned them */
 {
     if (snapshot_mesgs) {
         /* snapshot pointers are no longer in use */

win/tty/wintty.c

@@ -109,9 +109,9 @@ struct window_procs tty_procs = {
      | WC2_HILITE_STATUS | WC2_HITPOINTBAR | WC2_FLUSH_STATUS
      | WC2_RESET_STATUS
 #endif
-     | WC2_DARKGRAY | WC2_SUPPRESS_HIST | WC2_STATUSLINES),
+     | WC2_DARKGRAY | WC2_SUPPRESS_HIST | WC2_URGENT_MESG | WC2_STATUSLINES),
 #ifdef TEXTCOLOR
-    {1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1},   /* color availability */
+    {1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1}, /* color availability */
 #else
     {1, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 1},
 #endif
@@ -2662,7 +2662,13 @@ tty_putstr(winid window, int attr, const char *str)
 
     switch (cw->type) {
     case NHW_MESSAGE: {
-        int suppress_history = (attr & ATR_NOHISTORY);
+        int suppress_history = (attr & ATR_NOHISTORY),
+            urgent_message = (attr & ATR_URGENT);
+
+        /* if message is designated 'urgent' don't suppress it if user has
+           typed ESC at --More-- prompt when dismissing an earlier message */
+        if (urgent_message)
+            cw->flags &= ~WIN_STOP;
 
         /* in case we ever support display attributes for topline
            messages, clear flag mask leaving only display attr */