PygletWindowing backend ignores Retina scaling

[Jeremy Hill]

When creating a World(backend='pyglet') with or without acceleration, Retina scaling is ignored and effective resolution is halved.

Most things are at least internally self-consistent, but two noticeable exceptions are CaptureToTexture() (as used in Loupe()):

python -m Shady shell dynamic-range --backend=pyglet --acceleration=False

enhanced.scaling = 1

...and Capture():

gabor.Capture(saveas='blah.png')

The origin of this problem is that gabor.BoundingBox() returns a correct result in screen coordinates, but glCopyTexImage2D() and glReadPixels(), at the heart of CaptureToTexture() and Capture() respectively, work in actual pixels.