fix #H4246 - nasty() bugs

In theory nasty() could summon 200 critters at a time, although the
chance seems fairly remote.  But it was biased towards having lawfuls
summon more critters than others since there are fewer lawfuls in the
nasties[] list.  This puts a cap of 8 successful makemon() calls,
enough to completely surround the hero.  More than 8 monsters can be
generated, if any of the makemon() calls produces a group.  (I think
fire giants are the only thing in nasties[] that ever come in groups.)
It's still biased toward lawful summoners trying more times hoping to
produce a lawful creature and generating chaotic ones in the process.

The bug report also thought there was some problem between chaotic
and unaligned or with the Wizard, but unaligned is treated as if it
were chaotic (due to use of sgn() in the two or three places where
alignment type is manipulated) so that isn't an actual problem.

doc/fixes36.1

@@ -163,6 +163,8 @@ using 'R' on armor would bypass some restrictions imposed by 'T' (inner layer
 when examining hidden monsters (probing, persistent monster detection), tell
 	how they're hidden (under an object, on the ceiling, etc)
 some quest text corrections
+use a much tighter upper bound when summoning nasties; old method could
+	theoretically create 200 critters at a time
 
 
 Platform- and/or Interface-Specific Fixes