VirtualBox 4.2.0 RC3

# The following major new features were added:
- Improved Windows 8 support, in particular many 3D-related fixes
- GUI: VM groups
- GUI: expert mode for wizards
- GUI: allow to alter some settings during runtime
- Support for up to 36 network cards, in combination with an ICH9 chipset configuration
- Resource control: added support for limiting network IO bandwidth
- Added possibility to start VMs during system boot on Linux, OS X and Solaris
- Added experimental support for Drag'n'drop from the host to Linux guests. Support for more guests and for guest-to-host is planned.
- Added support for parallel port passthrough on Windows hosts
- Enhanced API for controlling the guest; please see the SDK reference and API documentation for more information
# In addition, the following items were fixed and/or added:
- Mac OS X hosts: sign application and installer to avoid warnings on Mountain Lion
- VMM: improved VM context switch performance for Intel CPUs using nested paging
- VMM: added support for FlushByASID features of AMD CPUs (Bulldozer and newer)
- VMM: fixed unreal mode handling on older CPUs with VT-x (gPXE, Solaris 7/8/9)
- VMM: fixed MP tables fixes for I/O APIC interrupt routing relevant for ancient SMP guests (e.g. old OS/2 releases)
- VMM: support recent VIA CPUs
- VMM: fixed handling of task gates if VT-x/AMD-V is disabled
- GUI: network operations manager
- GUI: allow taking screenshots of the current VM window content
- GUI: allow automatically sorting of the VM list
- GUI: allow starting of headless VMs from the GUI
- GUI: allow reset, shutdown and poweroff from the Manager window
- GUI: allow to globally limit the maximum screen resolution for guests
- GUI: show the full medium part on hovering the list of recently used ISO images
- GUI: do not create additional folders when a new machine has a separator character in its name
- GUI: don't crash on terminate if the settings dialog is still open
- GUI: consider scaled DPI values when display fonts on Windows hosts
- Snapshots: fixed a crash when restoring an old snapshot when powering off a VM
- Clipboard: disable the clipboard by default for new VMs. It can be enabled at any time using the VM menu.
- Settings: sanitise the name of VM folders and settings file
- Settings: allow to store the iSCSI initiator secret encrypted
- NAT: improvements for the built-in TFTP server
- E1000: 802.1q VLAN support
- Storage: implemented burning of audio CDs in passthrough mode
- Storage: fixed audio CD passthrough for certain media players
- Storage: implemented support for discarding unused image blocks through TRIM for SATA and IDE and UNMAP for SCSI when using VDI images
- Storage: added support for QED images
- Storage: added support for QCOW (full support for v1 and readonly support for v2 images)
- Storage: added readonly support for VHDX images
- Solaris additions: added support for X.org Server 1.11 and 1.12
- Solaris additions: switched to using an in-kernel mouse driver
- Windows hosts: no need to recreate host-only adapters after a VirtualBox update
- Windows hosts: updated toolchain; make the source code compatible to VC 2010 and enable some security-related compiler options