qemu: Update to 1.6.1

qemu 1.5.2 no longer works for me. I get "Device or resource busy" when I try to create a qemu machine with libvirt (on Linux 3.11). qemu 1.6.1 works fine, though.

However, there was some problem last time I tried updating to 1.6.0. A lot of Hydra builds failed. @edolstra How can I verify that 1.6.1 isn't broken in the same way?