explode() while engulfed (trunk only)

For an explosion caused by the player while the hero is engulfed,
skip adjacent monsters.  Also, don't give "you hear a blast" when an
unseen explosion is caused by a scroll of fire (explosion is always unseen
when hero is engulfed, regardless of explosion's cause).  [Offhand I'm
not sure whether something other than the player can trigger an explosion
while the hero is engulfed.]  Lastly, round up instead of down when a
monster takes half damage, so that non-zero can't be reduced to zero.

doc/fixes35.0

@@ -223,6 +223,7 @@ rogue's backstab bonus doesn't apply for throwing attacks
 hiding monsters who are unhidden when hero leaves a level can hide upon return
 touching a pile of objects while blind affects hero even when the pile is
 	big enough to give "there are many objects here" and not list them
+explosion while engulfed only affects engulfer and hero, not adjacent monsters
 
 
 Platform- and/or Interface-Specific Fixes