- Allow WM_WINDOWPOSCHANGING when the control is size 0 to set initial
  size.
- Combine multiple SetWindowPos calls in same processing line and make
  the flags like native.
- Redo WM_NCCALCSIZE to match native.
- Since Pager is a "transparent" control (except for its own buttons),
  the WM_ERASEBKGND needs to be passed to the parent. Also do the window
  offset like the native control does.