Decoupled canvas client dimensions from drawing buffer dimensions.
addressing minor issues with pull request
Fix #1160, and clear the canvas correctly.

The canvas used to be cleared by "resize" which would write
to the size even if it was unchanged.  Now that this is no
longer the case, it must be cleared manually.
Fixing issue where pick rays were miscomputed when the browser was zoomed
adding support for window.devicePixelRatio

Firefox 23 updates window.devicePixelRatio when zooming; Chrome 29 does
not. Chrome 31 does, but that's not stable yet.
Merge remote-tracking branch 'agi/master' into browser_zoom_fix

Conflicts:
	CHANGES.md
	Source/Scene/Camera.js
	Specs/Scene/CameraControllerSpec.js
billboard sizing fix
Merge pull request #1172 from AnalyticalGraphicsInc/issue1160

Fix #1160, and clear the canvas correctly.
Merge pull request #1162 from balefrost/browser_zoom_fix

Decoupled canvas client dimensions from drawing buffer dimensions.
Added Dan Yankowsky to CONTRIBUTORS.md
Tweak CHANGES.md
Merge branch 'master' into balloon