Packages (tar balls) installed with scripts/install.py do contain symbolic links.
Everything that they contain is written to the file installed.xml, and upon
uninstall attempted to remove.

However, the python script first tests if a file exists before it removes it
and uses os.path.exists for this, which only returns true when the target
is a file, or a symbolic link *pointing* to an existing file.

Since the removal of the tar ball elements is arbitrary, it is possible (and
often the case) that the file the symbolic link points to is removed before
the symbolic link itself is removed, causing the test to fail and the symbolic
link not to be removed.

This patch solves this bug by using os.path.lexists which returns true for
normal files when they exist, and true for symbolic links if they exist,
whether or not the file they point to exists, exactly what we want.

os.path.lexists was added to python 2.4, so that should not be problem.

This patch was originally tested to work several months ago, and has been in
use by the Imprudence TPV for a while now.