python-launchpadlib should use ~/.cache/launchpadlib for cache files

[Daniel Hahler]

launchpadlib should follow the XDG standard and use ~/.cache/launchpadlib for its cache files.

It looks like launchpadlib_dir needs to be adjusted and any existing data should/might get migrated from the old location.

% dpkg -L python-launchpadlib|xargs grep '\.launchpadlib'
/usr/share/pyshared/launchpadlib/launchpad.py: launchpadlib_dir = os.path.join('~', '.launchpadlib')
[...]

ProblemType: Bug
DistroRelease: Ubuntu 12.04
Package: python-launchpadlib 1.9.12-1
ProcVersionSignature: Ubuntu 3.2.0-32.51-generic 3.2.30
Uname: Linux 3.2.0-32-generic x86_64
ApportVersion: 2.0.1-0ubuntu14
Architecture: amd64
Date: Fri Oct 19 17:11:34 2012
InstallationMedia: Ubuntu 12.04 LTS "Precise Pangolin" - Release amd64 (20120425)
PackageArchitecture: all
SourcePackage: python-launchpadlib
UpgradeStatus: No upgrade log present (probably fresh install)