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

Pull request

v2:
 * Drop block/nfs patch since it exposes an unfinished QAPI interface [kwolf]

# gpg: Signature made Tue Jul  7 14:29:47 2015 BST using RSA key ID 81AB73C8
# gpg: Good signature from "Stefan Hajnoczi <[email protected]>"
# gpg:                 aka "Stefan Hajnoczi <[email protected]>"

* remotes/stefanha/tags/block-pull-request:
  blockjob: add block_job_release function
  block/raw-posix: Don't think /dev/fd/<NN> is a floppy drive.
  block: Use bdrv_drain to replace uncessary bdrv_drain_all
  block: Initialize local_err in bdrv_append_temp_snapshot
  block: update bdrv_drain_all()/bdrv_drain() comments
  qcow2: remove unnecessary check

Signed-off-by: Peter Maydell <[email protected]>