exploding wands

Pointed out by <Someone>:  engraving with a cursed wand should pose a
risk of having it explode just like zapping does.  [At the moment when one
explodes, any existing engraving doesn't get changed.]  Suggested by someone
(<Someone>?) some time back:  explosion due to recharging could be consolidated
with explosion due to zapping cursed wands.  And noted by <Someone> in the
newsgroup:  '+' in an engraving--perhaps written by someone trying to leave
bones file notes--should have a chance of being partially rubbed out to '-'.

include/extern.h

@@ -1711,6 +1711,7 @@ E void FDECL(forget_levels, (int));
 E void NDECL(forget_traps);
 E void FDECL(forget_map, (int));
 E int FDECL(seffects, (struct obj *));
+E void FDECL(wand_explode, (struct obj *,int));
 #ifdef USE_TRAMPOLI
 E void FDECL(set_lit, (int,int,genericptr_t));
 #endif