OK, as stopping or starting apache2 gives the XML error, I tried running startup.pl. And got:

perl /etc/apache2/startup.pl
Unable to recognise encoding of this document at /usr/share/perl5/XML/
+SAX/PurePerl/EncodingDetect.pm line 100.
Unable to recognise encoding of this document at /usr/share/perl5/XML/
+SAX/PurePerl/EncodingDetect.pm line 100.
Apache.pm was not loaded
 at /etc/apache2/startup.pl line 12
couldn't connect to dbi:Pg:dbname=xxxxx;host=localhost at /etc/apache2
+/startup.pl line 12.
[download]

Reduced startup.pl to

#!/usr/bin/env perl
use strict;
use warnings;
use lib '/usr/share/perl/5.10.0';
use ModPerl::Registry; # use Apache::Registry;
use Apache::DBI;
use Apache::AuthDBI;

Apache::DBI->connect_on_init('dbi:Pg:dbname=xxxxx;host=localhost', und
+ef, undef,
                { RaiseError => 1, AutoCommit => 1 })
        or
die "couldn't connect";

1;
[download]

and get

 perl  /etc/apache2/startup.pl
Apache.pm was not loaded
 at /etc/apache2/startup.pl line 13
couldn't connect at /etc/apache2/startup.pl line 13.
[download]

I'm closer to fixing the XML issue, but this one has me stumped! Let me know if this is veering off topic!