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

Tracing pull request

# gpg: Signature made Wed 07 May 2014 18:14:02 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:
  configure: Show trace output file conditionally
  trace: [tracetool] Minimize the amount of per-backend code
  trace: [simple] Bump up log version number
  trace: [tracetool] Change format docs to point to the generated file
  trace: [tracetool] Show list of frontends and backends sorted by name
  trace: [tracetool] Cosmetic changes
  trace: [tracetool] Spacing changes
  trace: [tracetool] Add methods 'Event.copy' and 'Arguments.copy'
  trace: [tracetool] Add method 'Event.api' to build event names

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