"Undo" and "Redo" are available when there's nothing to undo/redo

This bug was fixed in the package software-center - 2.1.0

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software-center (2.1.0) maverick; urgency=low

  [ Matthew McGowan ]
  * merged lp:~mmcg069/software-center/backforward-redraw-fix
  * make the overlaywithpixbuf cellrenderer inherit from a text
    cellrenderer, does away with the need to have 1px column in the
    appview for accessibility reasons.
    (lp:~mmcg069/software-center/overlay-w-pixbuf-tweak)
  * add nice animation to pathbar elements
    (lp:~mmcg069/software-center/pathbar-scroll-inn)

  [ Olivier Tilloy ]
  * fix LP: #564785:
    "each row has a progress bar (which itself never contains any text)"
  * show download completion status (LP: #460888)
  * add "bottom border" effect (LP: #439621)
  * add "history" GUI that reads /var/log/apt/history.log
  * Re-claim used memory after updating an existing AppStore with a
    new one (LP: #577540)
  * Fix the database update when run with a Turkish locale
    (patch by M. Vefa Bicakci). LP: #581207
  * Make buttons activate on mouse up, fix other inconsistencies
    in list view button operation (LP: #514835)

  [ Jacob Johan Edwards ]
  * merged lp:~j-johan-edwards/software-center/smooth_search, this
    massively improves the search and stops it from flickering
    (LP: #570682)
  * merged lp:~j-johan-edwards/software-center/action_bar that provides
    the foundation for the "custom packages list" branch
  * merged lp:~j-johan-edwards/software-center/unbranded_icons to
    provide a set of unbranded icons for e.g. Debian
  * merged lp:~j-johan-edwards/software-center/custom_lists to
    implement https://wiki.ubuntu.com/SoftwareCenter#Custom%20package%20lists

  [ Ken van Dine ]
  * allow sharing apps via gwibber and apturl
    (lp:~ken-vandine/software-center/sharing)

  [ Julian Andres Klode ]
  * merged lp:~juliank/software-center/debian that include fixes and
    updates for the new python-apt 0.8 API

  [ Kiwinote ]
  * data/featured.menu.in:
    - Update featured applications list per Desktop team (LP: #548534)
    - Feature 'fretsonfire-game' rather than 'fretsonfire' (LP: #538646)
  * softwarecenter/view/app.py:
    - Set correct sensitivity of 'edit > undo,redo,cut,copy,delete,select_all'
      (LP: #439613, LP: #530194)

  [ Michael Vogt ]
  * softwarecenter/view/appview.py:
    - simplify application list buildup and improve responsiveness
  * softwarecenter/view/*pane.py:
    - fix crash when ngettext is translated without %s format
      (LP: #449053)
  * add test/Makefile and ensure all tests are run in the bzr-buildpackage
    pre-build hook
  * softwarecenter/db/database.py, softwarecenter/view/appdetailsview.py:
    - add "StoreDatabase.get_iconname()" and use it
  * softwarecenter/view/appview.py:
    - small cleanups
  * softwarecenter/view/availablepane.py:
    - add iconnames when installing custom lists
  * softwarecenter/view/pendingview.py:
    - look for "appname" and "pkgname" (in this order) when showing
      the progress information
  * update about (LP: #566571)
  * merged lp:~apulido/software-center/mago_fix (many thanks to Ara Pulido)
  * data/unbranded-software-center.desktop.in:
    - add unbranded desktop file
  * softwar...