Merge remote-tracking branch 'remotes/qmp-unstable/tags/for-upstream' into staging

QMP pull request

# gpg: Signature made Mon May 11 14:15:19 2015 BST using RSA key ID E24ED5A7
# gpg: Good signature from "Luiz Capitulino <lcapitulino@gmail.com>"

* remotes/qmp-unstable/tags/for-upstream:
  scripts: qmp-shell: Add verbose flag
  scripts: qmp-shell: add transaction subshell
  scripts: qmp-shell: Expand support for QMP expressions
  scripts: qmp-shell: refactor helpers
  MAINTAINERS: New maintainer for QMP and QAPI
  json-parser: Accept 'null' in QMP
  qobject: Add a special null QObject
  qobject: Clean up around qtype_code
  QJSON: Use OBJECT_CHECK

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