fix bug #1332983

the universal superclass is a special-case for validate-superclass.
That has knock-on implications on its metaclass (can't be
built-in-class) which means we have to document an exception to
another part of AMOP.
Fix defknown of MAKE-RANDOM-STATE to avoid manual CHECK-TYPE.
Use NTH-VALUE when that's what is meant.
Simplify most uses of WITH-SYMBOL by altering its interface a little