new property: BLND_RES

Add enlightenment feedback for Sunsword's blocking of becoming blind
from light flashes.  It uses an extra property so that wizard mode
can report the reason.

EDITLEVEL is being incremented, so existing save and bones files are
invalidated.

src/mondata.c

@@ -187,7 +187,15 @@ resists_blnd(struct monst *mon)
     if (dmgtype_fromattack(ptr, AD_BLND, AT_EXPL)
         || dmgtype_fromattack(ptr, AD_BLND, AT_GAZE))
         return TRUE;
-    return resists_blnd_by_arti(mon);
+    /* Sunsword */
+    if (resists_blnd_by_arti(mon))
+        return TRUE;
+    /* catchall */
+    if (is_you && Blnd_resist) {
+        impossible("'Blnd_resist' but not resists_blnd()?");
+        return TRUE;
+    }
+    return FALSE;
 }
 
 /* True iff monster is resistant to light-induced blindness due to worn