roots method broken for root system lattices

[saliola]

This works:

sage: R = RootSystem(['A',2])
sage: R.ambient_lattice()
Ambient lattice of the Root system of type ['A', 2]
sage: R.ambient_lattice().roots()
[(1, -1, 0), (1, 0, -1), (0, 1, -1), (-1, 1, 0), (-1, 0, 1), (0, -1, 1)]
sage: 

But this method does not work for any of the other associated lattices.

sage: R = RootSystem(['A',2])
sage: R.coroot_lattice().roots()
---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
...
AttributeError: 'RootSpace' object has no attribute 'positive_roots'
sage: R.coweight_lattice().roots()
---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
...
AttributeError: 'WeightSpace' object has no attribute 'positive_roots'
sage: R.root_lattice().roots()
---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
...
AttributeError: 'RootSpace' object has no attribute 'positive_roots'
sage: R.weight_lattice().roots()
---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
...
AttributeError: 'WeightSpace' object has no attribute 'positive_roots'