Merge remote-tracking branch 'remotes/armbru/tags/pull-qobject-2018-07-27-v2' into staging

QObject patches for 2018-07-27 (3.0.0-rc3)

# gpg: Signature made Sat 28 Jul 2018 08:10:39 BST
# gpg:                using RSA key 3870B400EB918653
# gpg: Good signature from "Markus Armbruster <armbru@redhat.com>"
# gpg:                 aka "Markus Armbruster <armbru@pond.sub.org>"
# Primary key fingerprint: 354B C8B3 D7EB 2A6B 6867  4E5F 3870 B400 EB91 8653

* remotes/armbru/tags/pull-qobject-2018-07-27-v2:
  qstring: Move qstring_from_substr()'s @end one to the right
  qstring: Assert size calculations don't overflow
  qstring: Fix qstring_from_substr() not to provoke int overflow

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