Cache(rootdir) needs to be absolute

Binary package hint: python-apt

Hi

When instanciating an apt.Cache with a rootdir, it will break if it's not absolute:
mkdir -p apt-test/etc/apt
cp /etc/apt/sources.list* -a apt-test/etc/apt
% python

Python 2.7.2rc1 (default, May 31 2011, 11:34:02)
[GCC 4.6.1] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import apt
>>> apt.Cache(rootdir='apt-test')
creating: apt-test/var/lib/dpkg
creating: apt-test/var/cache/apt/archives/partial
creating: apt-test/var/lib/apt/lists/partial
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib/python2.7/dist-packages/apt/cache.py", line 93, in __init__
    self.open(progress)
  File "/usr/lib/python2.7/dist-packages/apt/cache.py", line 136, in open
    self._cache = apt_pkg.Cache(progress)
SystemError: E:Could not open file apt-test/var/lib/apt/apt-test/var/lib/dpkg/status - open (2: No such file or directory), E:The package lists or status file could not be parsed or opened.

this with oneiric, apt 0.8.14.1ubuntu5 and python-apt 0.8.0~exp4ubuntu1.

apt.conf RootDir and python-apt's Cache.__doc__ don't say rootdir needs to be absolute; perhaps some piece of apt is broken WRT to rootdir, perhaps python-apt should make the path absolute, or perhaps the docs need to be updated to require an absolute dir.

Cheers,