AxisArrays allows repeated values in axis

It seems that AxisArrays doesn't check that the names in an axis are unique. The MWE currently works and it seems it shouldn't

MWE

julia> ax1 = fill(randstring(10), 100);
julia> t = AxisArray(rand(100, 48), ax1, 1:48);
julia> t
2-dimensional AxisArray{Float64,2,...} with axes:
    :row, ["YF263D1vZG", "YF263D1vZG", "YF263D1vZG", "YF263D1vZG", "YF263D1vZG", "YF263D1vZG", "YF263D1vZG", "YF263D1vZG", "YF263D1vZG", "YF263D1vZG"  …  "YF263D1vZG", "YF263D1vZG", "YF263D1vZG", "YF263D1vZG", "YF263D1vZG", "YF263D1vZG", "YF263D1vZG", "YF263D1vZG", "YF263D1vZG", "YF263D1vZG"]
    :col, 1:48
And data, a 100×48 Array{Float64,2}:
 0.544045   0.706665  0.794698   …  0.146636   0.173689   0.860602
 0.818773   0.665337  0.598364      0.318264   0.779036   0.49364
 0.506061   0.634103  0.429253      0.727027   0.280061   0.105964
 0.188533   0.438404  0.205067      0.803538   0.469894   0.706383
 0.232693   0.520553  0.731804      0.483673   0.0525813  0.735506
 0.708654   0.495217  0.419302   …  0.187662   0.394126   0.286807
 0.0296371  0.145384  0.67488       0.363728   0.976938   0.679723
 0.736628   0.130968  0.583726      0.295144   0.465268   0.2539
 0.537004   0.585194  0.204467      0.491539   0.428528   0.259942
 0.884711   0.496042  0.0305943     0.0416132  0.279033   0.792419
 ⋮                               ⋱  ⋮                     
 0.161877   0.163169  0.645313      0.978483   0.168679   0.731583
 0.0828598  0.774799  0.987582      0.466019   0.214213   0.757673
 0.333942   0.919552  0.512247      0.420129   0.268359   0.412811
 0.843079   0.416188  0.821125      0.0913968  0.298315   0.681747
 0.137244   0.171126  0.953037   …  0.272229   0.2507     0.822746
 0.0817602  0.75145   0.767151      0.988747   0.458262   0.584586
 0.674519   0.518633  0.91036       0.255896   0.724942   0.637565
 0.360949   0.11814   0.974368      0.24273    0.957803   0.365758
 0.497645   0.396735  0.0457641     0.511115   0.099716   0.0692743

Start by reproducing the Julia MWE from the issue and trace AxisArray construction and axis validation to find where repeated axis values are accepted. Done means the behavior is rejected consistently and a regression test covers the repeated-name case.