Accessibility: Show a message when monster is spotted

Adds a new boolean option, spot_monsters.  If on, every time
the hero notices a monster which was out of sight before,
a message is given.  Combine with accessiblemsg to get the
monster location:

(3north): You see a newt.

Breaks saves and bones.

include/extern.h

@@ -1074,6 +1074,8 @@ extern boolean test_move(coordxy, coordxy, coordxy, coordxy, int);
 extern int wiz_debug_cmd_traveldisplay(void);
 #endif
 extern boolean u_rooted(void);
+extern void notice_mon(struct monst *) NONNULLARG1;
+extern void notice_all_mons(boolean);
 extern void impact_disturbs_zombies(struct obj *, boolean) NONNULLARG1;
 extern void disturb_buried_zombies(coordxy, coordxy);
 extern boolean u_maybe_impaired(void);

include/flag.h

@@ -191,8 +191,20 @@ struct debug_flags {
 struct accessibility_data {
     boolean accessiblemsg; /* use msg_loc for plined messages */
     coord msg_loc;         /* accessiblemsg: location */
+    boolean mon_notices;   /* msg when hero notices a monster */
+    int mon_notices_blocked; /* temp disable mon_notices */
 };
 
+/* Use notice_mon_off() / notice_mon_on() to temporarily disable
+   noticing the monsters in the vision code - perhaps the game
+   needs to output some other messages in between.
+   Call notice_all_mons() afterwards to catch up. */
+#define notice_mon_off() do { a11y.mon_notices_blocked++; } while(0)
+#define notice_mon_on()  do { if (--a11y.mon_notices_blocked < 0) { \
+            impossible("mon_notices_blocked<0");                    \
+            a11y.mon_notices_blocked = 0;                           \
+        } } while(0)
+
 /*
  * Stuff that really isn't option or platform related and does not
  * get saved and restored.  They are set and cleared during the game

include/monst.h

@@ -160,6 +160,8 @@ struct monst {
     Bitfield(mtemplit, 1);  /* temporarily seen; only valid during bhit() */
     Bitfield(meverseen, 1); /* mon has been seen at some point */
 
+    Bitfield(mspotted, 1);  /* mon is currently seen by hero */
+
 #define MAX_NUM_WORMS 32    /* should be 2^(wormno bitfield size) */
 
     unsigned long mstrategy; /* for monsters with mflag3: current strategy */

include/optlist.h

@@ -654,6 +654,9 @@ static int optfn_##a(int, int, boolean, char *, char *);
     NHOPTB(sparkle, Map, 0, opt_out, set_in_game,
            On, Yes, No, No, NoAlias, &flags.sparkle, Term_False,
            "display sparkly effect when resisting magic")
+    NHOPTB(spot_monsters, Advanced, 0, opt_in, set_in_game,
+           Off, Yes, No, No, NoAlias, &a11y.mon_notices, Term_False,
+           "message when hero spots a monster")
     NHOPTB(splash_screen, Advanced, 0, opt_out, set_in_config,
            On, Yes, No, No, NoAlias, &iflags.wc_splash_screen, Term_False,
            (char *)0)

include/patchlevel.h

@@ -17,7 +17,7 @@
  * Incrementing EDITLEVEL can be used to force invalidation of old bones
  * and save files.
  */
-#define EDITLEVEL 96
+#define EDITLEVEL 97
 
 /*
  * Development status possibilities.