Avoid calling method on example group class

Without this a `NoMethodError` is raised:

    undefined method `call' for :next_runnable_index_for:Symbol

Author: dgmstuart

lib/rspec/core/example.rb

@@ -180,7 +180,7 @@ def initialize(example_group_class, description, user_metadata, example_block=ni
 
         @metadata = Metadata::ExampleHash.create(
           @example_group_class.metadata, user_metadata,
-          example_group_class.method(:next_runnable_index_for),
+          lambda { |file| example_group_class.next_runnable_index_for(file) },
           description, example_block
         )
 

spec/rspec/core/example_spec.rb

@@ -797,4 +797,20 @@ def expect_pending_result(example)
       expect(example.reporter).to be reporter
     end
   end
+
+  it 'allows extensions to add `method` to the DSL without causing problems' do
+    http_testing_extension = Module.new do
+      attr_reader :http_method
+      def method(meth); @http_method = meth; end
+    end
+
+    describe_successfully do
+      extend http_testing_extension
+      method :get
+
+      it "allows `method` to specify the HTTP method" do
+        expect(self.class.http_method).to eq(:get)
+      end
+    end
+  end
 end