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

Four little fixes

# gpg: Signature made Fri Apr 24 19:56:51 2015 BST using RSA key ID E24ED5A7
# gpg: Good signature from "Luiz Capitulino <lcapitulino@gmail.com>"

* remotes/qmp-unstable/tags/for-upstream:
  qmp: Give saner messages related to qmp_capabilities misuse
  qmp-commands: fix incorrect uses of ":O" specifier
  qapi: Drop dead genlist parameter
  balloon: improve error msg when adding second device

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