Merge remote-tracking branch 'remotes/stefanha/tags/tracing-pull-request' into staging

Merge remote-tracking branch 'remotes/stefanha/tags/tracing-pull-request' into staging

Tracing pull request

# gpg: Signature made Mon 09 Jun 2014 14:44:18 BST using RSA key ID 81AB73C8
# gpg: Good signature from "Stefan Hajnoczi <stefanha@redhat.com>"
# gpg:                 aka "Stefan Hajnoczi <stefanha@gmail.com>"

* remotes/stefanha/tags/tracing-pull-request:
  trace: Replace fprintf with error_report and print location
  trace: Multi-backend tracing
  trace: Replace error with warning if event is not defined
  simpletrace: add support for trace record pid field
  trace: add pid field to simpletrace record

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