[WINLOGON][WIN32K]

[WINLOGON][WIN32K]
Move the shutdown privilege check from winlogon to win32k (function "UserInitiateShutdown") as it should be done.

[WIN32K]
- Introduce the pair of UserInitiateShutdown/UserEndShutdown calls that should be called when WINSRV starts a shutdown (and when it finishes it). In particular it is in UserInitiateShutdown that we need to check whether the caller has the rights to perform a shutdown (it should also have a valid window station).
- Remove the ROS-specific TWOPARAM_ROUTINE_EXITREACTOS call that is traded for Win2k3-compatible call to UserInitiateShutdown.

[WINSRV]
Hackfix our current ExitWindowsEx functionality (based on a patch by Alex made against r46050 for win32csr) to make it "compatible" with the improvements in win32k: impersonate the caller and call the UserInitiateShutdown win32k system call (instead of the TWOPARAM_ROUTINE_EXITREACTOS). More will come later on.

[USER32]
Win32k can require performing shutdown in an asynchronous way (needed also on WINSRV side) so we need to put all the code in a worker thread.

Part 8/X (part 6 was r65693 and part 7 was r66186).

CORE-8322 #comment Start to add Alex' win32csr shutdown patch in WINSRV; fixes for winlogon and additions to win32k.

svn path=/trunk/; revision=66192