figure out what to do about h5py dtype having metadata.vlen in order to get pynwb validator to work with Lindi

[magland]

See #47

and see code comments here

lindi/lindi/LindiH5pyFile/LindiH5pyDataset.py

Lines 95 to 125 in d269450

	if ret.kind == 'O':
	if not ret.metadata:
	# The following correction is needed because of
	# this code in hdmf/backends/hdf5/h5tools.py:
	# def _check_str_dtype(self, h5obj):
	# dtype = h5obj.dtype
	# if dtype.kind == 'O':
	# if dtype.metadata.get('vlen') == str and H5PY_3:
	# return StrDataset(h5obj, None)
	# return h5obj
	# We cannot have a dtype with kind 'O' and no metadata
	# There is also this section in pynwb validator.py
	# if isinstance(received, np.dtype):
	# if received.char == 'O':
	# if 'vlen' in received.metadata:
	# received = received.metadata['vlen']
	# else:
	# raise ValueError("Unrecognized type: '%s'" % received)
	# received = 'utf' if received is str else 'ascii'
	# elif received.char == 'U':
	# received = 'utf'
	# elif received.char == 'S':
	# received = 'ascii'
	# else:
	# received = received.name
	# ------------------------------------------
	# I don't know how to figure out when vlen should be str or bytes
	# but validate seems to work only when I put in vlen = bytes
	#
	vlen = bytes
	ret = np.dtype(str(ret), metadata={'vlen': vlen})