Healers may get tiny damage increase with knives

Styled as anatomy knowledge, a healer attacking a monster in melee
with a knife gets +1 damage per 6 dead monsters of that type,
capped at +3 damage.

Handwaving away the fact we're not keeping track who actually
killed the monsters...

Idea from aosdict.

doc/fixes3-7-0.txt

@@ -1578,6 +1578,7 @@ slow monster effects are more effective against faster enemies
 light-spell is clerical, if playing a priest
 boomerang can hit multiple monsters
 the "bustling town" minetown has more peacefuls
+healers may get tiny damage increase when attacking with knives
 
 
 Fixes to 3.7.0-x General Problems Exposed Via git Repository

src/weapon.c

@@ -319,6 +319,10 @@ dmgval(struct obj *otmp, struct monst *mon)
         }
     }
 
+    /* Healer with anatomy knowledge */
+    if (Role_if(PM_HEALER) && objects[otmp->otyp].oc_skill == P_KNIFE)
+        tmp += min(3, svm.mvitals[monsndx(ptr)].died / 6);
+
     /* Put weapon vs. monster type damage bonuses in below: */
     if (Is_weapon || otmp->oclass == GEM_CLASS || otmp->oclass == BALL_CLASS
         || otmp->oclass == CHAIN_CLASS) {