PM queue lockups in the Qt frontend

[Valery V. Sedletski]

When the Selector window is running together with the VM window, the PM queue lockups are observed. If you move a window, or press keyboard, the GUI freezes and locks up the PM. The beeps on the speaker are heard. Also, the window interiors are not updated for some time. But usually, when OS is booted, the GUI unlocks. If you try running the Qt frontend without the selector window (by running it as "VirtualBox.exe --startvm <vmname>"), the VM runs much more smoothly. It looks like the VM and the selector window communicate, and if the selector window is not running, the communication disappears, and thus, no PM lockup related problems. We need to investigate this.