Merge remote-tracking branch 'remotes/armbru/tags/pull-error-2015-09-10' into staging

error: On abort, report where the error was created

# gpg: Signature made Thu 10 Sep 2015 13:01:39 BST using RSA key ID EB918653
# gpg: Good signature from "Markus Armbruster <[email protected]>"
# gpg:                 aka "Markus Armbruster <[email protected]>"

* remotes/armbru/tags/pull-error-2015-09-10:
  error: On abort, report where the error was created
  error: Revamp interface documentation
  error: error_set_errno() is unused, drop
  qga/vss-win32: Document the DLL requires non-null errp
  qga: Clean up unnecessarily dirty casts
  error: Make error_setg() a function
  error: De-duplicate code creating Error objects

Signed-off-by: Peter Maydell <[email protected]>