Small collision optimizations.
Ternary operator style fixes on FlxObject and FlxQuadTree.
FlxMouse: properly clean up signal listener in destroy()
Made better use of resolveGroup() in FlxQuadTree.add
Indentation fix.
Made better use of resolveGroup() in FlxQuadTree.add pt 2
Merge pull request #1009 from gamedevsam/collision_optimizations

Small collision optimizations.