added app-emulation/virtualbox-guest-additions from official tree.
app-emulation/virtualbox-guest-additions: added FreeBSD support.
added x11-drivers/xf86-video-virtualbox from official tree.
x11-drivers/xf86-video-virtualbox: added FreeBSD support.
added dev-util/kbuild from official tree.
dev-util/kbuild: added FreeBSD support.
dev-util/kbuild: fix Manifest