Merge remote-tracking branch 'remotes/sstabellini/tags/xen-2016-04-20' into staging

Xen 2016/04/20

# gpg: Signature made Wed 20 Apr 2016 12:08:56 BST using RSA key ID 70E1AE90
# gpg: Good signature from "Stefano Stabellini <stefano.stabellini@eu.citrix.com>"

* remotes/sstabellini/tags/xen-2016-04-20:
  xenfb: use the correct condition to avoid excessive looping

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