upgrade qt4 to 4.6.4

5x as big as 4.3.4, however nothing builds against 4.3.
since newer versions are even more bloated (+50 MB for every major
release), 4.6 should be good enough to get most qt apps working.
linux.config: enable KVM and add some defaults

this page has further options that may be useful to turn on:
http://www.linux-kvm.org/page/Tuning_Kernel
eudev: allow access to /dev/kvm for kvm group
qemu: explicitly build with kvm support
add aqemu frontend
su: update to latest (fixes prompt display)
add qemu-kvm