Merge remote-tracking branch 'remotes/stefanha/tags/block-pull-request' into staging

Block pull request

# gpg: Signature made Mon 23 Jun 2014 09:53:49 BST using RSA key ID 81AB73C8
# gpg: Good signature from "Stefan Hajnoczi <stefanha@redhat.com>"
# gpg:                 aka "Stefan Hajnoczi <stefanha@gmail.com>"

* remotes/stefanha/tags/block-pull-request:
  block: asynchronously stop the VM on I/O errors
  vl: allow other threads to do qemu_system_vmstop_request
  sheepdog: fix NULL dereference in sd_create
  QemuOpts: check NULL opts in qemu_opt_get functions
  block: m25p80: Support read only bdrvs.
  block: m25p80: sync_page(): Deindent function body.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>