fix U193 - digging feedback for undiggable trees

> Zapping a wand of digging at trees in ranger's quest gives a message
> "rock glows then fades".

     There was code to handle this, but it didn't work due to the
definition of IS_TREE making checks for STONE be sensitive to code
ordering (STONE was checked first in this case).

#define IS_TREE(typ)    ((typ) == TREE || \
                        (level.flags.arboreal && (typ) == STONE))

Why is it defined this way?  Shouldn't STONE simply be converted
into TREE when arboreal levels get created?

doc/fixes34.1

@@ -330,6 +330,7 @@ non-moving monster are not affected by liquid
 'A' command behaved differently depending on menustyle when non-weapons were
 	present in the quiver or alternate weapon inventory slots
 most cases of the hero dropping things need to check for dropping on an altar
+zapping undiggable trees with wand or spell of dig gave feedback about rock
 
 
 Platform- and/or Interface-Specific Fixes