OSX issues when using HI-DPI mode.

[mdsitton]

So by default (as the code currently is) for HI-DPI display modes on OSX the code renders properly, but at the resolution targeted by the hi-dpi mode. So a 200x200 window on 1280x800 high dpi would show as 200x200, but each pixel would be rendered on 4 pixels, with no extra data so it looks pixelated.

When the high dpi flag is added to the sdl2 window code the following happens
https://dl.dropboxusercontent.com/u/37405488/hidpimode.png

The item attached to the cursor is no longer following properly(need to scale the mouse coords i think). And the rendering is way off.

[mdsitton]

Here are some other oddities
If i move the window, everything adapts to the highdpi mode and just works o.0?
https://dl.dropboxusercontent.com/u/37405488/hidpiworking.png

here is regular no highdpi for comparison:
https://dl.dropboxusercontent.com/u/37405488/hidpino.png