Rename SlotDefinition to Slot

And the derived XXDefinitions to XXSlot

Just to be more consistent
And possibly free the Definition for the Language side

test/sol/class_send/test_class_instance.rb

@@ -53,11 +53,11 @@ module Sol
       assert_equal SlotLoad,  @ins.class
     end
     def test_left
-      assert_equal MessageDefinition , @ins.left.class
+      assert_equal MessageSlot , @ins.left.class
       assert_equal [:return_value] , @ins.left.slots
     end
     def test_right
-      assert_equal MessageDefinition , @ins.right.class
+      assert_equal MessageSlot , @ins.right.class
       assert_equal [:receiver , :inst] , @ins.right.slots
     end
   end

test/sol/class_send/test_class_send_inherited.rb

@@ -31,7 +31,7 @@ module Sol
     def test_receiver
       assert_equal SlotMachine::ArgumentTransfer,  @ins.next(1).class
       assert_equal 0,  @ins.next(1).arguments.length
-      assert_equal ObjectDefinition,  @ins.next(1).receiver.class
+      assert_equal ObjectSlot,  @ins.next(1).receiver.class
       assert_equal Parfait::Class,  @ins.next(1).receiver.known_object.class
       assert_equal :Space,  @ins.next(1).receiver.known_object.name
     end

test/sol/class_send/test_send_class.rb

@@ -34,12 +34,12 @@ module Sol
       assert_equal MessageSetup , @ins.class , @ins
     end
     def test_receiver
-      assert_equal SlotDefinition,  @ins.next.receiver.class
+      assert_equal Slot,  @ins.next.receiver.class
       assert_equal Parfait::Class,  @ins.next.receiver.known_object.class
       assert_equal :Object ,  @ins.next.receiver.known_object.name
     end
     def test_receiver_move
-      assert_equal ObjectDefinition,  @ins.next.receiver.class
+      assert_equal ObjectSlot,  @ins.next.receiver.class
     end
     def test_receiver
       assert_equal Parfait::Class,  @ins.next.receiver.known_object.class