one statue from single vampire via cockatrice corpse

one statue from single vampire via cockatrice corpse

 Changes to be committed:
	modified:   doc/fixes36.1
	modified:   include/extern.h
	modified:   src/mon.c

Fixes H4148 (bz246) and H4150 (bz248)

comments:
I wielded a c-corpse against a shapeshifting vampire bat (checked with a
stethoscope, it said "shapeshifter".) The bat turned to stone and spawned a
vampire.  I hit the vampire and it also turned to stone, so I had two statues
from one monster (vampire bat and vampire.)  Not sure if this is a bug or a
feature...

comments:
Engulfed by a fog cloud that was actually a Vampire,
and got the message: "You break out of the vampire!"