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

# gpg: Signature made Fri 25 Sep 2015 16:47:31 BST using RSA key ID C0DE3057
# gpg: Good signature from "Jeffrey Cody <[email protected]>"
# gpg:                 aka "Jeffrey Cody <[email protected]>"
# gpg:                 aka "Jeffrey Cody <[email protected]>"

* remotes/cody/tags/block-pull-request:
  sheepdog: refine discard support
  sheepdog: use per AIOCB dirty indexes for non overlapping requests
  Backup: don't do copy-on-read in before_write_notifier
  block: Introduce a new API bdrv_co_no_copy_on_readv()
  sheepdog: add reopen support
  block/nfs: cache allocated filesize for read-only files
  block/nfs: fix calculation of allocated file size

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