wand/spell/breath killer reason

Extend "killed by the touch of death inflicted by <monster>" to buzz().
"Killed by a bolt of cold" becomes "killed by a bolt of cold zapped by
<monster>" or "killed by a blast of cold" becomes "killed by a blast
of cold exhaled by <monster>" and so forth.

More work than expected; the zap code isn't passed enough context.

BZ_M_WAND() was producing the wrong value for wands zapped by monsters.

src/decl.c

@@ -252,6 +252,9 @@ const struct instance_globals_b g_init_b = {
     UNDEFINED_PTR, /* bbubbles */
     /* pickup.c */
     FALSE, /* bucx_filter */
+    /* zap.c */
+    NULL, /* buzzer -- monst that zapped/cast/breathed to initiate buzz() */
+
     TRUE, /* havestate*/
     IVMAGIC  /* b_magic to validate that structure layout has been preserved */
 };