Can't slice an redim'ed DynamicMap

[basnijholt]

The following doesn't work

dmap = hv.DynamicMap(lambda X, Y: hv.Scatter([(X,Y)]), kdims=['X', 'Y']).redim.values(X=[0, 1, 2], Y=[2, 3, 4])
hv.HoloMap(dmap[:, :])

it only prints

:HoloMap   [X,Y]

This will fix qt/adaptive/issues/113

[philippjfr]

@jlstevens I know we explicitly didn't allow this when we simplified DynamicMap a while ago but I think there is good reason to expand [:] into all the values if they are defined on the dimension. Having to define the values twice just to sample the space seems redundant and quite a hassle.