dist-upgrade failed: apache2 postinst failed on absolute symlinks in mods-enabled

I tried to upgrade from 12.04 LTS to 14.04 LTS using "do-release-upgrade". The system had previously (a few minutes previously) been upgraded from 10.04 LTS to 12.04 LTS. As far as I can tell, the first upgrade was successful, but the second failed when trying to configure apache2:

disable obsolete module dav_fs
Module dav_fs disabled.
disable obsolete module dav
ERROR: The following modules depend on dav and need to be disabled first: dav_svn
dpkg: error processing package apache2 (--configure):
 subprocess installed post-installation script returned error exit status 1
No apport report written because MaxReports has already been reached
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Please report this bug in a browser at
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and attach the files in /var/log/dist-upgrade/ to the bug report.
installArchives() failed

I think this is caused by the fact that I have absolute symlinks in /etc/apache2/mods-enabled:

root@sigurd:/home/bjh21# ls -o /etc/apache2/mods-enabled/dav*
lrwxrwxrwx 1 root 36 Nov 12 2012 /etc/apache2/mods-enabled/dav.load -> /etc/apache2/mods-available/dav.load
lrwxrwxrwx 1 root 30 Nov 12 2012 /etc/apache2/mods-enabled/dav_svn.conf -> ../mods-available/dav_svn.conf
lrwxrwxrwx 1 root 40 Nov 12 2012 /etc/apache2/mods-enabled/dav_svn.load -> /etc/apache2/mods-available/dav_svn.load

The code that detects obsolete modules in apache2.postinst looks like it will (accidentally) not work with absolute symlinks:

refresh_modules()
{
        if we_are_upgrading_from_wheezy $@ && [ -d /etc/apache2/mods-enabled/ ] ; then
                shopt -s nullglob
                for link in /etc/apache2/mods-enabled/*.load ; do
                        target=$(readlink "$link") || true
                        if [ -z "$target" ] ; then
                                continue
                        fi

                        module=$(basename "$link" | sed 's/\.load//') || true

                        if [ ! -e "/etc/apache2/mods-enabled/$target" ] ; then
                                echo "disable obsolete module $module"
                                a2dismod -m -q "$module"

etc.

Concatenating the symlink contents with the directory name only works for relative symlinks. A simpler approach would be simply to check the link for existence, which will treat broken links as non-existent:

if [ ! -e "${link}" ]; then