[ntoskrnl]

[ntoskrnl]
- Implement calling OkayToCloseProcedure callouts to win32k for desktop and window station objects
- Fix a bug that caused ObpCloseHandle to return success even when OkayToCloseProcedure failed

[win32k]
- Rewrite SetProcessWindowStation to actually set the current window station and close the previous one
- Implement OkayToCloseProcedure callouts from the kernel to prevent closing the current desktop or window station

svn path=/trunk/; revision=51115