Fixed deadlock in back-to-back reduce_scatters.

Change-Id: I92d32b15e516a39710b676aee692ae9b70638937
Reviewed-on: http://git-master/r/935458
Reviewed-by: Przemek Tredak <ptredak@nvidia.com>
Tested-by: Przemek Tredak <ptredak@nvidia.com>

.gitignore

@@ -1 +1,2 @@
+# Copyright (c) 2015-2016, NVIDIA CORPORATION. All rights reserved.
 /build