Merge remote-tracking branch 'remotes/armbru/tags/pull-error-2016-02-09' into staging

Error reporting patches for 2016-02-09

# gpg: Signature made Tue 09 Feb 2016 12:38:33 GMT using RSA key ID EB918653
# gpg: Good signature from "Markus Armbruster <armbru@redhat.com>"
# gpg:                 aka "Markus Armbruster <armbru@pond.sub.org>"

* remotes/armbru/tags/pull-error-2016-02-09:
  HACKING: Add a section on error handling and reporting
  error: Improve documentation some more
  Use error_fatal to simplify obvious fatal errors (again)

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