Fixed for response stubbing with headers for streaming responses.

Fixes amazon-archives/aws-sdk-core-ruby#220

aws-sdk-core/lib/seahorse/client/plugins/restful_bindings.rb

@@ -69,7 +69,9 @@ def parse_response(response)
                 status_code = response.context.http_response.status_code
                 response.data[key] = status_code
               when 'header'
-                response.data[key] = extract_header(headers, shape)
+                if headers.key?(shape.location_name)
+                  response.data[key] = extract_header(headers, shape)
+                end
               when 'headers'
                 response.data[key] = extract_header_map(headers, shape)
               end

aws-sdk-core/spec/aws/stubbing/stub_spec.rb

@@ -195,13 +195,15 @@ module ClientStubs
 
           it 'stubs the HTTP response target when with streaming APIs' do
             s3 = S3::Client.new(stub_responses: true)
-            s3.stub_responses(:get_object, { body: 'data' })
+            s3.stub_responses(:get_object, { body: 'data', content_length: 4 })
             io = StringIO.new
             resp = s3.get_object(bucket:'bucket', key:'key', response_target: io)
             expect(resp.body.read).to eq('data')
             expect(resp.body).to be(io)
             expect(resp.context.http_response.body).to be(io)
+            expect(resp.content_length).to eq(4)
           end
+
         end
       end
     end