IOContext(io::IOContext, ctx::IOContext) does not include context variables from io

[fonsp]

This behaviour seems unintuitive to me:

julia> left = IOContext(devnull, :a => 1);

julia> right = IOContext(devnull, :b => 2);

julia> io = IOContext(IOContext(devnull, :a => 1), IOContext(devnull, :b => 2));

julia> get(io, :a, "not found")
"not found"

julia> get(io, :b, "not found")
2