Winston fails to plot when pre-compiled

[vtjnash]

With JuliaLang/julia#5821, Winston fails to show plots because it does runtime work while compiling Winston.jl (related to JuliaLang/julia#1268)

2549 if !isdefined(Main, :IJulia)
2550     if output_surface == :gtk
2551         include("gtk.jl")
2552         display(::WinstonDisplay, p::PlotContainer) = gtk(p)
2553     elseif output_surface == :tk
2554         include("tk.jl")
2555         display(::WinstonDisplay, p::PlotContainer) = tk(p)
2556     else
2557         assert(false)
2558     end
2559     pushdisplay(WinstonDisplay())
2560 end

[JeffBezanson]

A lot of packages are going to have to move code like this into init functions.