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

# gpg: Signature made Wed Jul 22 12:43:35 2015 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:
  AioContext: optimize clearing the EventNotifier
  AioContext: fix broken placement of event_notifier_test_and_clear
  AioContext: fix broken ctx->dispatching optimization
  aio-win32: reorganize polling loop
  tests: remove irrelevant assertions from test-aio
  qemu-timer: initialize "timers_done_ev" to set
  mirror: Speed up bitmap initial scanning

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