Delay inclusion of LetDefinitions module.

It needs to be included last so that its definitions can take precedence
in case of a name collision.

lib/rspec/core/example_group.rb

@@ -237,6 +237,13 @@ def self.subclass(parent, args, &example_group_block)
         subclass = Class.new(parent)
         subclass.set_it_up(*args)
         subclass.module_eval(&example_group_block) if example_group_block
+
+        # The LetDefinitions module must be included _after_ other modules
+        # to ensure that it takes precendence when there are name collisions.
+        # Thus, we delay including it until after the example group block
+        # has been eval'd.
+        subclass.send(:include, MemoizedHelpers.module_for(subclass))
+
         subclass
       end
 

lib/rspec/core/memoized_helpers.rb

@@ -469,7 +469,6 @@ def self.module_for(example_group)
             }
           end
 
-          example_group.__send__(:include, mod)
           example_group.const_set(:LetDefinitions, mod)
           mod
         end