message.
- Organize WM_NOTIFY processing in preparation for Unicode
- Implement TBN_GETDISPINFO and I_IMAGECALLBACK for bitmaps.
- Implement drawing of separator for TBSTYLE_DROPDOWN similar to native.
- Change drawing of buttons to support TBSTYLE_LIST and make match
  native pixel layout (with and without bitmaps).
- Change TOOLBAR_MeasureString to measure with DrawText like native.
  This eliminates extra space due to prefix char ("&").
- Speed up TOOLBAR_CalcStrings by doing the HDC and FONT selection once.
- Change calc of buttons to match drawing for TBSTYLE_LIST and
  separators.