Refactor the Win32 event dispatcher

There are a couple of outstanding problems with the Win32 event dispatcher:

1. SOLVED - the use of multimedia timers on WinXP is not thread-safe and can cause crashes (task 146591)
2. SOLVED - these fast timers are implementing using postEvent(), which causes problems when the event loop is re-entered (task 134783). Specifically, the post event list grows indefinitely.
3. Qt posted events are not sent while Windows spins a modal loop, e.g. when showing a native dialog or when the user moves or resizes the window (task 108764)
4. zero-timers and/or constantly posting new events can starve other event sources (task 97086)

The ideal would be an event dispatcher that uses a standard message pump, so that a minimum amount of code is needed to integrate Qt with other toolkits. At the moment, ActiveQt installs a hook to call QApplication::sendPostedEvents(0, -1) (the -1 is wrong, I have a task for that - SOLVED), and it would be nice to get rid of that. This would ease the development of the Visual Studio and Eclipse integrations.