Simplify container implementation to add/remove children, and ensure that load/unload aren’t called when they shouldn’t be.
Fixes windows problems re-using controls as it would call OnUnLoad too many times and keep the layout suspended
Mac: Fix Label on os x < 10.7
Wpf: Fix Bitmap.Clone when the bitmap is loaded from a file
WinForms: DockContainer should only suspend layout, not redraw when not loaded (no need to suspend drawing as its not visible)