VirtualBox 4.0.8.71778

* Mac OS X hosts: fixed incompatibility with recent Mac OS X versions in 64-bit mode
* Mac OS X hosts: fixed incompatibility with hosts with more than 16 cores
* Mac OS X hosts: fixed painting corruptions on a second monitor in 64-bit mode
* GUI: restored functionality to set an empty host key to disallow any host key combination
* VBoxManage: added controlvm screenshotpng subcommand for saving the screenshot of a running VM in PNG format
* VBoxHeadless: fixed potential crash during shutdown (Windows hosts only)
* NAT: built-in services use the correct Ethernet addresses in Ethernet header and in ARP requests
* Host-only networking: fixed adapter reference counting
* E1000: fixed rare guest crashes with Linux SMP guests
* SATA: fixed guest disk corruption under rare circumstances (only relevant for guests with more than 2GB RAM;
* Storage: fixed data corruption after a snapshot was taken with asynchronous I/O enabled
* Floppy: several improvement
* HPET: another fix for time jumps
* USB: removed assumption that string descriptors are null-terminated (Windows hosts only)
* 3D support: fixed a potential crash when resizing the guest window
* 3D support: fixed GNOME 3 rendering under Ubuntu 11.04 and Fedora 15
* Snapshots: fixed another bug which could lose entries in the media registry when restoring a snapshot
* Shared Folders: don't stop mounting the other valid folders if one host folder is inaccessible
* Linux Additions: check whether gcc and make are installed before building kernel modules
* Solaris Additions: added support for X.Org Server 1.10
* Guest Additions: fixed inappropriate Guest Additions update notification when using vendor-specific version suffixes