Many lists and trees are inaccessible

[James Teh]

Many list and tree controls used in VirtualBox 2.x are inaccessible. Under Windows, an IAccessible object is created, but it has a role of ROLE_SYSTEM_CLIENT and no other useful properties, which suggests that QT doesn't know how to make it accessible. These controls include:

• The list of machines on the Details tab of the main window
• Both controls (trees?) on the Snapshots tab of the main window
• The control (list?) on the Description tab of the main window

Note that these controls were previously accessible in VirtualBox 1.6.x, so this is a regression.