disclosing genocided/extinct monsters

Make the handling of unique monsters consistent between vanquished
monsters and genocided/extinct monsters.  No visible difference to
players.

This also prevents Nazgul and erinys from being polymorphed into
some other form to reduce the chance that their kill count fails
to match the expected number when they're reported to be extinct.
[My long test game (with 3451 total dead critters as of the last
save file) used for exercising the sorting of vanquished monsters
included
 120 soldiers
 111 wolves
   9 Nazgul
   2 erinyes
and the genocided/extinct list had none genocided, those four
extinct.  No doubt the missing third erinys was alive somewhere
rather than counted as something else after getting polymorphed,
so this band-aid wouldn't have helped this particular game.]

src/makemon.c

@@ -1326,6 +1326,11 @@ int
 mbirth_limit(mndx)
 int mndx;
 {
+    /* There is an implicit limit of 4 for "high priest of <deity>",
+     * but aligned priests can grow into high priests, thus they aren't
+     * really limited to 4, so leave the default amount in place for them.
+     */
+
     /* assert(MAXMONNO < 255); */
     return (mndx == PM_NAZGUL ? 9 : mndx == PM_ERINYS ? 3 : MAXMONNO);
 }