fix pull request #479 - statues of stoning-immunes

Statues on Medusa's level are supposed to be from petrified creatures
rather than somebody's artwork, so creatures that can't be turned to
stone aren't eligible.  However, creatures who change form when hit
with stoning damage (foo golems to stone golem) were being allowed.
Also, statues in cockatrice nest rooms are supposed to be from former
characters and take their names from the high scores file.  But when
'record' is empty, the statue would be of a random creature instead
of being changed into a player character, so both not the latter and
possibly something that can't be petrified.

I've taken the Medusa part as-is but did the cockatrice nest part
differently.  It rejected statues of non-stonable creatures in case
the named character attempt failed.  I've changed things so that when
a named player character can't be created, it will use an unnamed one
instead of random creature.  The issue of maybe ending up with a non-
stonable form goes away because all player characters are vulnerable.

Fixes #479

doc/fixes37.0

@@ -428,6 +428,11 @@ poly'd hero who exploded when attacking a monster didn't wake up other
 	woke other monsters within different radius than same monster's would
 troll corpse revival was inhibited by hero wielding Trollsbane; do that if
 	anyone on level is wielding it
+statues representing petrified creatures on Medusa's level might be from
+	monsters who change form (golems) when hit with stoning damage
+attempt to make corpse or statue of a named player character would yield that
+	of a random monster instead when 'record' was empty; could result in
+	statues of non-stonable creatures in cockatrice nests
 
 
 Fixes to 3.7.0-x Problems that Were Exposed Via git Repository