X.axis_name[groups] do not work anymore (regression in 0.30)

[gdementen]

>>> arr = ndtest(10)
>>> groups = (X.a['a1':], X.a[:'a8'])
>>> X.a[groups]
AttributeError                            Traceback (most recent call last)
[...]
AttributeError: _Axis__mapping
>>> groups = (arr.a['a1':], arr.a[:'a8'])
>>> X.a[groups]
AttributeError                            Traceback (most recent call last)
[...]
AttributeError: _Axis__mapping

This works though:

>>> arr.a[groups]
 (a['a1':], a[:'a8'])

[gdementen]

Note that this bug only triggers when the name of the AxisReference is the same as the original group (i.e. when the operation was useless).

For example, in the above example, this worked fine:

>>> X.b[groups]
(X.b['a1':], X.b[:'a8'])