pyfive: test failure on groups

[bnlawrence]

As it stands, pyfive branch commit 04ae240 fails in test_h5netcdf_pyfive at

    assert set(ds.groups) == set(["subgroup"])

where the debugger tells me that
set(ds.groups) = {'enum_t', 'subgroup'} instead of {subgropu}

Suspect that'll be to do with my various hacks for Datatype and check_enum_dtype ... to investigate.

[bnlawrence]

The debugger tells me that in the h5py normal version, ds.groups in advance of the set looks like this:

ds.groups
{'subgroup': <class 'netCDF4._netCDF4.Group'>
group /subgroup:
    dimensions(sizes): y(10)
    va...2 subvar(x), float64 y_var(y)
    groups: }
special variables
function variables
'subgroup':
<class 'netCDF4._netCDF4.Group'>
group /subgroup:
    dimensions(sizes): y(10)
    variables(dimensions): int32 subvar(x), float64 y_var(y)
    groups: 
len():
1
set(ds.groups)
{'subgroup'}

By contrast, in advance of the set, in the pyfive version, it looks like this:

ds.groups
Frozen(<h5netcdf.core._LazyObjectLookup object at 0x106c934d0>)

[bnlawrence]

It turns out this was a problem with enumerations which are not supported by pyfive, but were being erroneously treated as groups (my pyfive issue #8).