pull request #1092 - monster blindness

Pull request from entrez:  a monster can become permanently blind via
camera flash but being hit by vapors from thrown potion of blindness
would set a blindness countdown timer and blindness would be cured
when that expired.

Closes #1092

include/monst.h

@@ -248,6 +248,8 @@ struct monst {
 #define engulfing_u(mon) (u.uswallow && (u.ustuck == (mon)))
 #define helpless(mon) ((mon)->msleeping || !(mon)->mcanmove)
 
+#define mon_perma_blind(mon) (!mon->mcansee && !mon->mblinded)
+
 #define mon_offmap(mon) (((mon)->mstate & (MON_DETACH|MON_MIGRATING|MON_LIMBO|MON_OFFMAP)) != 0)
 
 /* Get the maximum difficulty monsters that can currently be generated,

src/mondata.c

@@ -226,6 +226,10 @@ can_blnd(
     if (!haseyes(mdef->data))
         return FALSE;
 
+    /* if monster has been permanently blinded, the deed is already done */
+    if (!is_you && mon_perma_blind(mdef))
+        return FALSE;
+
     /* /corvus oculum corvi non eruit/
        a saying expressed in Latin rather than a zoological observation:
        "a crow will not pluck out the eye of another crow"

src/potion.c

@@ -1786,7 +1786,7 @@ potionhit(struct monst *mon, struct obj *obj, int how)
             mon_adjust_speed(mon, 1, obj);
             break;
         case POT_BLINDNESS:
-            if (haseyes(mon->data)) {
+            if (haseyes(mon->data) && !mon_perma_blind(mon)) {
                 int btmp = 64 + rn2(32)
                             + rn2(32) * !resist(mon, POTION_CLASS, 0, NOTELL);