Ubuntu system image 2.2

2.2 (2014-03-05)
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 * When `CheckForUpdate()` is called a second time, while an auto-download is
   in progress, but after the first check is complete, we send an
   `UpdateAvailableStatus` signal with the cached information. (LP: #1284217)
 * Close a race condition when manually downloading and issuing multiple
   `CheckForUpdate` calls. (LP: #1287919)
 * Support disabling either the HTTP or HTTPS services for update (but not
   both). The ``[service]http_port`` or ``[service]https_port`` may be set to
   the string ``disabled`` and the disabled protocol will fall back to the
   enabled protocol. Implementation given by Vojtech Bocek. (LP: #1278589)
 * Allow the channel.ini file to override the ``[service]`` section.
 * Now that ubuntu-download-manager performs atomic renames of temporary
   files, system-image no longer needs to do that. (LP: #1287287)
 * When an exception in the state machine occurs while checking for updates,
   the exception is caught and logged. When using the CLI, the result is an
   exit code of 1. When using the D-Bus API, an `UpdateAvailableStatus`
   signal is sent with `error_reason` set to the exception string. This
   exception is *not* propagated back to GLib. (LP: #1250817)
 * Log directory path is passed to ubuntu-download-manager to assist in
   debugging. Given by Manuel de la Peña. (LP: #1279532)