Removed the whole store**HWND spiel. No longer works properly (nil pointers woo).
Fixed a small error in group_windows.go.
Removed containerResize() from container_windows.c; it no longer exists.
Storing the *container in the Windows GWLP_USERDATA is no longer needed; strip it.
Added the sharedWndProc() spiel to Tab now that it stores Controls directly. Will need to add the same to Group.
More TODOs.
Actually we don't need to do anything to Tab right nwo...
More TODOs for real.
Fixed preferred size forgetfulness.