Empty window pops up when plotting

On @JeffBezanson's computer, whenever he makes a new plot with PyPlot, an empty window pops up.

Start by reproducing the issue in PyPlot.jl when creating a new plot, comparing behavior on the reported computer with other environments. Inspect the interaction between PyPlot.jl and matplotlib.pyplot and determine what causes the empty window; done means new plots no longer open an unintended empty window.

索引モデルが issue の本文から書いたものです。