Key normalization broke Plots backend

[BeastyBlacksmith]

885888e broke the possibility to nest Options like in

Options(Options("solid" => nothing) => nothing, "draw opacity" => 1.0)

I can fix that in the next Plots release by using

merge(Options("solid" => nothing), Options("draw opacity" => 1,0))

but technically I would also need to retro-cap the older versions.

[tpapp]

I think that the first version ever worked was an overlooked corner case, the recommended API is merge (and always has been, for a given value of always).