killer_xname changes (trunk only)

killer_xname changes (trunk only)

     Have killer_xname() handle corpses properly and also avoid having it
use user-supplied fruit names as per <Someone>'s suggestion.  Also make
a start at eliminating the umpteen inconsitent checks for whether a monster
type (like "Oracle") ought to be prefixed by "the ".

     I used a stub which looped over all object types, all artifacts, and
corpses of all monster types to print the output of killer_xname() for each
one; its prefix choice among {[no article], a, an, the} looked right.