silver vs poly'd hero (trunk only)

<Someone> reported that thitu() was adding d20 damage for silver object
hitting silver-hating hero even though all the callers were using dmgval()
which also does that, resulting in doubled silver bonus/penalty.  This
fixes that (including for boomerangs thrown by player, which weren't using
dmgval(), to handle a hyptothetical silver boomerang).  While testing it,
I noticed that there was no "the silver sears your flesh" message when a
monster hit you with a wielded silver weapon, so this fixes that too.
(How did we miss that?  And how did <Someone>? :-)

doc/fixes35.0

@@ -134,6 +134,8 @@ eating gold in front of the vault guard will make the guard angry
 calculate engulf time differently for non-digestion attacks than for digestion
 preform autopickup and/or report on objects at the spot when a failed #untrap
 	attempt causes the hero to move onto a trap's location
+thrown silver weapon hitting silver-hating poly'd hero got double silver damage
+wielded silver weapon hitting silver-hating poly'd hero lacked silver message
 
 
 Platform- and/or Interface-Specific Fixes