message: Allow tf.summary.merge_all() assign operation name
  One may need to assign name of the MergeSummary operation
diff: @@ -285,7 +285,7 @@ def merge(inputs, collections=None, name=None):
  @tf_export('summary.merge_all')
  -def merge_all(key=_ops.GraphKeys.SUMMARIES, scope=None):
  +def merge_all(key=_ops.GraphKeys.SUMMARIES, scope=None, name=None):
  """Merges all summaries collected in the default graph.
  Args:
  @@ -314,7 +314,7 @@ def merge_all(key=_ops.GraphKeys.SUMMARIES, scope=None):
  if not summary_ops:
  return None
  else:
  - return merge(summary_ops)
  + return merge(summary_ops, name=name)
  @tf_export('summary.get_summary_description')
  