lzop was removed due to some confusion over whether it provided functional
advantages distinct from xz. This has been addressed in the mailing list post
archived at http://permalink.gmane.org/gmane.comp.emulators.libvirt/16487, and
support for lzop is re-added here.

* libvirt.spec.in: add dependancy on lzop
* src/qemu.conf: update documentation of save_image_format
* src/qemu_driver.c: re-add lzop compression option