add-apt-repository generates useless save files

[Edward Z. Yang]

When I run 'add-apt-repository', the script generates a save file for /etc/apt/sources.list and every file /etc/apt/sources.list.d. This is completely pointless, because add-apt-repository doesn't (and shouldn't) touch *any* of these files; it should simply add a new file to /etc/apt/sources.list.d.

ProblemType: Bug
DistroRelease: Ubuntu 13.10
Package: software-properties-common 0.92.28
ProcVersionSignature: Ubuntu 3.11.0-14.21-generic 3.11.7
Uname: Linux 3.11.0-14-generic x86_64
NonfreeKernelModules: openafs
ApportVersion: 2.12.5-0ubuntu2.1
Architecture: amd64
Date: Fri Dec 20 15:30:58 2013
EcryptfsInUse: Yes
InstallationDate: Installed on 2013-11-21 (29 days ago)
InstallationMedia: Ubuntu 13.10 "Saucy Salamander" - Release amd64 (20131016.1)
MarkForUpload: True
PackageArchitecture: all
SourcePackage: software-properties
UpgradeStatus: No upgrade log present (probably fresh install)

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.

[Anders Kaseorg (andersk)]

Unfortunately, it actually does touch all of those files—it bumps all their timestamps to the present. This destroys valuable forensic information for future me trying to figure out when and why I added these PPAs.