Upgrading Ubuntu to new version deletes previous wallpapers

Still needs done in Update Manager
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1. When upgrading from 11.10, update-manager should also install ubuntu-wallpapers-oneiric. When upgrading from 10.04, update-manager should also install ubuntu-wallpapers-lucid
2. All ubuntu-wallpapers* packages should be marked as manually installed so that they won't be automatically removed when upgrading to the next Ubuntu release.

Original bug report
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As mentioned on this forum thread, upgrading Ubuntu deletes the previous wallpapers. This is bad because apparently if someone had set their wallpaper to say a Natty community wallpaper, they would get a black background on updating to Oneiric with no easy way to get their old wallpaper back. http://ubuntuforums.org/showthread.php?t=1852257

This is also very bad because Ubuntu updates aren't supposed to mess with user preferences.

I suggest that the old wallpapers be kept in the ubuntu-wallpapers source package. A new ubuntu-wallpapers metapackage should be created that depends on ubuntu-wallpapers-oneiric. That dependency just gets updated for each release. Users who have ubuntu-wallpapers-natty installed won't lose them when they upgrade their install ubuntu-wallpapers. Those who do a clean install of Ubuntu Oneiric can still install the Natty wallpapers if they want them (which is good because some people do a clean install just because they think it's better).

ProblemType: BugDistroRelease: Ubuntu 11.10
Package: ubuntu-wallpapers 0.32.1
ProcVersionSignature: Ubuntu 3.0.0-12.19-generic 3.0.4
Uname: Linux 3.0.0-12-generic x86_64
ApportVersion: 1.23-0ubuntu2
Architecture: amd64
Date: Fri Sep 30 13:50:24 2011
PackageArchitecture: allSourcePackage: ubuntu-wallpapers
UpgradeStatus: No upgrade log present (probably fresh install)