Implement session management

[Dmitry A. Kuminov]

Session management in OS/2 is basically detecting when the PM is about to shutdown and providing a way to cancel it. On the Qt side, it's QSessionManager and a couple of methods in QApplication.

[pmw]

I guess this would include implementation of QApplication::isSessionRestored(). I have to comment out that part in KDiff3 at the moment.

[Dmitry A. Kuminov]

I hope you do so using #ifndef QT_NO_SESSIONMANAGER/#endif rather than // or or #ifdef 0.

[Dmitry A. Kuminov]

Committed the QSessionManager implementation in r428.

Notes:

1. The only function it does on OS/2 is inform the application about the system shutdown through QApplication::commitData() (note that QApplication::saveState() is never called on OS/2). This functionality corresponds to Qt for Windows.

2. QSessionManager::cancel() cannot cancel the XWorkplace Extended Shutdown procedure at the moment. In order to be able to do so, a patch needs to be applied to XWorkplace (see the attachment). We always call WinCancelShutdown() if QSessionManager::cancel() was called though so it should cancel the standard system shutdown procedure (used when no XWP is installed or when Extended Shutdown is disabled).

[Dmitry A. Kuminov]

XWorkplace patch that makes it possible to programmatically cancel extended shutdown