Merge branch 'for-anthony' of git://repo.or.cz/qemu/kevin

* 'for-anthony' of git://repo.or.cz/qemu/kevin:
  Add qcow2 documentation
  hw/xen_disk: aio_inflight not released in handling ioreq when nr_segments==0
  Improve error handling in do_snapshot_blkdev()
  Fix ATA SMART and CHECK POWER MODE
  Don't allow multiwrites against a block device without underlying medium
  tools: Use real async.c instead of stubs
  Add error message for loading snapshot without VM state
  block/qcow: Don't ignore immediate read/write and other failures
  block/vdi: Don't ignore immediate read/write failures