monster birth limits exceeded by bones load

Bones loading was only checking to see if a
monster was marked extinct, it wasn't adding
up the born count of a species in the current
game with the number of that species on the
bones level being loaded. That made it possible
to exceed the correct number of nazgul and
erinys via bones.

This adds a common routine called propagate()
that makemon() and restmonchn(ghostly) share,
for incrementing the born count and checking for
extinction, etc.

When a bones level is loaded, restmonchn()
will flag an illegal monster (duplicated unique,
or too many of a species) by setting the
individual monster's mhpmax to the cookie
value DEFUNCT_MONSTER. Before getbones() finishes
loading the bones level, it will purge those
monsters from the chain.

doc/fixes34.3

@@ -7,6 +7,7 @@ polymorphing to a flaming sphere should cure slime like other flaming monsters
 grammar, spelling and other typos
 student statues were converted to valkyries, not archeologists
 fix typo in bustling town down stairs declaration
+you could exceed the limits on nazgul and erinys counts via bones files
 
 
 Platform- and/or Interface-Specific Fixes