Hackiness of InvertedIndexIterator printing

[phipsgabler]

It's a really minor thing, but displaying InvertedIndexIterator as Not (cf. this line) made it really hard for me to find out how to convert an inverted index to a normal one...

julia> r
3×3 Array{Float64,2}:
 0.103825   0.287749  0.720987
 0.0868532  0.938357  0.445691
 0.526585   0.753124  0.0108292

julia> to_indices(r, (Not(2), :)) # huh?
(Not(2), Base.Slice(Base.OneTo(3)))

julia> collect(to_indices(r, (Not(2), :))[1]) # aha! this is _not_ Not!
2-element Array{Int64,1}:
 1
 3

I agree that it's somewhat superior to writing out the whole word InvertedIndexIterator, but the confusion with InvertedIndex is there. Perhaps add the picks to the printout?