about dialog no longer existent after clicking 'x'

This bug was fixed in the package software-center - 3.1.2

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software-center (3.1.2) natty; urgency=low

  [ Michael Vogt ]
  * merged lp:~kiwinote/software-center/getting-the-small-things-right,
    many thanks!
  * test/test_where_is_it.py, test/data/fake-applications.menu:
    use test/data/fake-applications.menu in the test_where_is_it.py
    that points to <LegacyDir>/usr/share/app-install/desktop</LegacyDir>
    to ensure the "where-is-it" tests work on all machines
  * test/test_appdetails_view.py:
    - add better message on missing python-mock
  * softwarecenter/enums.py:
    - add DB_SCHEMA_VERSION as metadata to the DB and ensure we rebuild
      the local DB on mismatch (the systemwide one is handlded already)
  * softwarecenter/db/update.py, utils/update-software-center:
    - do no longer log to the root logger but instead to a db.update logger
  * test/test_mime.py:
    - use the local DB in the test and build it if needed
  * setup.py:
    - add "lint" target that runs pocketlint
  * softwarecenter/apt/apthistory.py, softwarecenter/db/application.py:
    - do lazy loading in the constructor in a idle_add() function
  * test/test_database.py:
    - update test for lazy loading
  * softwarecenter/view/historypane.py:
    - ensure the lazy loaded history is ready before displaying it
  * test/Makefile, .bzr-builddeb/default.conf:
    - add clean target and run it on bzr-buildpackage

  [ Kiwinote ]
  * softwarecenter/app.py:
    - don't delete about dialog upon closing the window (LP: #658678)
  * softwarecenter/db/application.py:
    - icon should return '?' icon if pkg is not found
    - fix logic in determining when the source is available, ie don't show
      'use this source' if source is already enabled
  * softwarecenter/db/update.py:
    - don't index desktop files not available for our arch (LP: #629434)
      (most visible example in partners channel on maverick amd64)
  * softwarecenter/view/appdetailsview_gtk.py:
    - pkg_state must be queried before querying the title in order to get the
      correct 'not found' title
    - _update_minimal must update title in order to enable source based on
      app-install-data info, but then realise that the pkg isn't available
      due to outdated app-install-data info (4pkgs for maverick final)
    - _update_minimal must update description when we have just enabled a
      source instead of continuing to display an empty description
  * softwarecenter/view/catview_gtk.py:
    - don't append the recommended category to self.departments - this causes
      the recommended category button to be displayed on maximising window
  * clean up some 'is it available for our architecture' code that is not
    needed anymore (idealy we don't need the info in the db either)
  * <all>:
    - don't pass the history object throughout the panes, but load on demand
  * softwarecenter/app.py:
    - update the file menu on demand
    - import & load history_pane on demand
    - import login related stuff on demand to save startup time
  * softwarecenter/db/application.py:
    - don't show the installation date immediately if it means taking 9s
      to determine it

  [ Gary Lask...