[WIN32K:NTUSER]
- Cleanup window clipboard data while the window still exists and is not dereferenced.
- When a window is about to be destroyed (just before we send the WM_DESTROY message), if it is the current clipboard owner, make it release the clipboard. The WM_RENDERALLFORMATS message is then sent, and if needed, one WM_DRAWCLIPBOARD message.
- Send a WM_DRAWCLIPBOARD message when SetClipboardViewer is called.
WM_DRAWCLIPBOARD messages are sent as notifications to the corresponding windows.
svn path=/trunk/; revision=70744