rename singleton_class to single_class and misc

was clashing with real ruby method name
also many superclass mismatch fixes
some misc

lib/vool/class_method_expression.rb

@@ -12,11 +12,11 @@ module Vool
     # Must pass in the actual Parfait class (default nil is just to conform to api)
     def to_parfait( clazz = nil )
       raise "No class given to class method #{name}" unless clazz
-      clazz.add_instance_method_for(name , make_arg_type , make_frame , body )
+      clazz.single_class.add_instance_method_for(name , make_arg_type , make_frame , body )
     end
 
     def to_mom(clazz)
-      raise "not singleton" unless clazz.class == Parfait::SingletonClass
+      raise "not singleton #{clazz.class}" unless clazz.class == Parfait::SingletonClass
       raise( "no class in #{self}") unless clazz
       method = clazz.get_instance_method(name )
       raise( "no class method in #{@name} in #{clazz}") unless method