Macosx canvas

Hello,  finally with the macosx build, I want to expose those issues :
* On Display.(re)create(), canvas still overlaps other components (setLayer bounds)
* A JVM NullPointerException is eventually thrown upon Display.destroy()
* The Context bounds are the hi-resolution ones, and affect user coordinate systems.

Illustrating the problem on my small app :
![lwjgl-canvas-on](https://cloud.githubusercontent.com/assets/5566338/4510183/e8e86cf0-4b27-11e4-886c-40b0a6e7dd7f.png)

So here's my mods..
It's essentially about the coordinate system and context retain/release calls.
A correction about a Keystroke event (Right-Left mismatch).
A correction about mouse coordinates rounding.

cu 
@b23prodtm