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

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

# gpg: Signature made Wed 28 Sep 2016 19:15:22 BST
# gpg:                using RSA key 0x9CA4ABB381AB73C8
# gpg: Good signature from "Stefan Hajnoczi <stefanha@redhat.com>"
# gpg:                 aka "Stefan Hajnoczi <stefanha@gmail.com>"
# Primary key fingerprint: 8695 A8BF D3F9 7CDA AC35  775A 9CA4 ABB3 81AB 73C8

* remotes/stefanha/tags/block-pull-request:
  linux-aio: fix re-entrant completion processing
  test-coroutine: test qemu_coroutine_entered()
  coroutine: add qemu_coroutine_entered() function
  libqos: fix qvring_init()
  iothread: check iothread->ctx before aio_context_unref to avoid assertion
  aio-posix: avoid unnecessary aio_epoll_enabled() calls
  block: mirror: fix wrong comment of mirror_start

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