rename singleton_class to single_class and misc

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

test/parfait/test_singleton_class.rb

@@ -5,7 +5,7 @@ module Parfait
 
     def setup
       super
-      @try = @space.create_class( :Try , :Object).singleton_class
+      @try = @space.create_class( :Try , :Object).single_class
     end
 
     def test_type_forclass