explorer.exe: Implement SC_SCREENSAVE by starting xdg-screensaver (try 2)

[Paul Chitescu]

Changelog:
        explorer.exe: Implement SC_SCREENSAVE by starting xdg-screensaver with 
option to lock the screen.

The desktop window reacts to SC_SCREENSAVE by starting the screen saver, just 
like it happens in Windows. No action is taken (and returns FALSE) if running 
in a virtual desktop.

Alternatively, a non-zero lparam is used to signal that the screen should be 
locked. This cooperates with the user32.dll patch that implements 
LockWorkStation(). This is an extension, there is no equivalent in Windows 
but all the programs I've seen that trigger the system screen saver set 
lparam=0.

Thanks to Steven Edwards (winehacker at gmail.com) for the idea of 
using "xdg-screensaver lock" to implement LockWorkStation.


Previous patch had a copy/paste problem: int pid = pid = ...