merge 2.6.0 to trunk
diff --git a/python/setup.py b/python/setup.py
index 6eecd48..9441d0e 100755
--- a/python/setup.py
+++ b/python/setup.py
@@ -138,10 +138,9 @@
 
 if __name__ == '__main__':
   ext_module_list = []
-  nocpp = '--nocpp_implementation'
-  if nocpp in sys.argv:
+  cpp_impl = '--cpp_implementation'
+  if cpp_impl in sys.argv:
     sys.argv.remove(cpp_impl)
-  else:
     # C++ implementation extension
     ext_module_list.append(Extension(
         "google.protobuf.pyext._message",