Allow knife and stiletto as possible tin opening tools

Via Dynahack, original idea from K-mod by Karadoc.

doc/fixes36.1

@@ -100,6 +100,7 @@ dissolve iron bars by force-fighting with wielded potion of acid
 poison breath leaves a trail of poison gas
 make vault guard accept names starting with number
 fix weight of containers in special levels
+allow knife and stiletto as possible tin opening tools
 
 
 Platform- and/or Interface-Specific Fixes

src/eat.c

@@ -1431,6 +1431,8 @@ struct obj *otmp;
         case ELVEN_DAGGER:
         case ORCISH_DAGGER:
         case ATHAME:
+        case KNIFE:
+        case STILETTO:
         case CRYSKNIFE:
             tmp = 3;
             break;