message: Issue Origin:
  The hardcoded forward slash value for _SHARDED_SUFFIX broke on windows since the windows file system does not except forward slashes.
diff: @@ -317,7 +317,7 @@ class BaseSaverBuilder(object):
  # prefix directly, instead of any physical pathname. (On failure and
  # subsequent restore, an outdated and orphaned temporary directory can be
  # safely removed.)
  - _SHARDED_SUFFIX = "_temp_%s/part" % uuid.uuid4().hex
  + _SHARDED_SUFFIX = os.path.normpath("_temp_%s/part" % uuid.uuid4().hex)
  tmp_checkpoint_prefix = string_ops.string_join(
  [checkpoint_prefix, _SHARDED_SUFFIX])
  